It may be a regression caused by this recent change:
---
commit 61d478c71c5341cdc54e6bfb4ace4252852fd972
Author: Christian Heimes <christian@python.org>
Date:   Sat Jan 27 15:51:38 2018 +0100

    bpo-31399: Let OpenSSL verify hostname and IP address (#3462)
    
    bpo-31399: Let OpenSSL verify hostname and IP
    
    The ssl module now uses OpenSSL's X509_VERIFY_PARAM_set1_host() and
    X509_VERIFY_PARAM_set1_ip() API to verify hostname and IP addresses.
    
    * Remove match_hostname calls
    * Check for libssl with set1_host, libssl must provide X509_VERIFY_PARAM_set1_host()
    * Add documentation for OpenSSL 1.0.2 requirement
    * Don't support OpenSSL special mode with a leading dot, e.g. ".example.org" matches "www.example.org". It's not standard conform.
    * Add hostname_checks_common_name
    
    Signed-off-by: Christian Heimes <christian@python.org>
---

Travis CI output, reformatted to make it more readable:

https://travis-ci.org/python/cpython/jobs/334652437

test_check_hostname (test.test_ftplib.TestTLS_FTPClass) ...

Exception in thread Thread-83:
Traceback (most recent call last):
  File "/home/travis/build/python/cpython/Lib/asynchat.py", line 251, in initiate_send
    num_sent = self.send(data)
  File "/home/travis/build/python/cpython/Lib/test/test_ftplib.py", line 381, in send
    return super(SSLConnection, self).send(data)
  File "/home/travis/build/python/cpython/Lib/asyncore.py", line 360, in send
    result = self.socket.send(data)
  File "/home/travis/build/python/cpython/Lib/ssl.py", line 963, in send
    return self._sslobj.write(data)
  File "/home/travis/build/python/cpython/Lib/ssl.py", line 670, in write
    return self._sslobj.write(data)
ssl.SSLError: [SSL: SSLV3_ALERT_BAD_CERTIFICATE] sslv3 alert bad certificate (_ssl.c:2206)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/travis/build/python/cpython/Lib/asyncore.py", line 83, in read
    obj.handle_read_event()
  File "/home/travis/build/python/cpython/Lib/test/test_ftplib.py", line 369, in handle_read_event
    super(SSLConnection, self).handle_read_event()
  File "/home/travis/build/python/cpython/Lib/asyncore.py", line 422, in handle_read_event
    self.handle_read()
  File "/home/travis/build/python/cpython/Lib/asynchat.py", line 171, in handle_read
    self.found_terminator()
  File "/home/travis/build/python/cpython/Lib/test/test_ftplib.py", line 116, in found_terminator
    method(arg)
  File "/home/travis/build/python/cpython/Lib/test/test_ftplib.py", line 231, in cmd_list
    self.dtp.push(LIST_DATA)
  File "/home/travis/build/python/cpython/Lib/test/test_ftplib.py", line 73, in push
    super(DummyDTPHandler, self).push(what.encode('ascii'))
  File "/home/travis/build/python/cpython/Lib/asynchat.py", line 202, in push
    self.initiate_send()
  File "/home/travis/build/python/cpython/Lib/asynchat.py", line 253, in initiate_send
    self.handle_error()
  File "/home/travis/build/python/cpython/Lib/test/test_ftplib.py", line 402, in handle_error
    raise Exception
Exception

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/travis/build/python/cpython/Lib/threading.py", line 917, in _bootstrap_inner
    self.run()
  File "/home/travis/build/python/cpython/Lib/test/test_ftplib.py", line 279, in run
    asyncore.loop(timeout=0.1, count=1)
  File "/home/travis/build/python/cpython/Lib/asyncore.py", line 207, in loop
    poll_fun(timeout, map)
  File "/home/travis/build/python/cpython/Lib/asyncore.py", line 150, in poll
    read(obj)
  File "/home/travis/build/python/cpython/Lib/asyncore.py", line 87, in read
    obj.handle_error()
  File "/home/travis/build/python/cpython/Lib/test/test_ftplib.py", line 402, in handle_error
    raise Exception
Exception

ERROR

======================================================================
ERROR: test_check_hostname (test.test_ftplib.TestTLS_FTPClass)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/build/python/cpython/Lib/test/test_ftplib.py", line 958, in test_check_hostname
    self.client.quit()
  File "/home/travis/build/python/cpython/Lib/ftplib.py", line 665, in quit
    resp = self.voidcmd('QUIT')
  File "/home/travis/build/python/cpython/Lib/ftplib.py", line 278, in voidcmd
    return self.voidresp()
  File "/home/travis/build/python/cpython/Lib/ftplib.py", line 251, in voidresp
    resp = self.getresp()
  File "/home/travis/build/python/cpython/Lib/ftplib.py", line 236, in getresp
    resp = self.getmultiline()
  File "/home/travis/build/python/cpython/Lib/ftplib.py", line 222, in getmultiline
    line = self.getline()
  File "/home/travis/build/python/cpython/Lib/ftplib.py", line 204, in getline
    line = self.file.readline(self.maxline + 1)
  File "/home/travis/build/python/cpython/Lib/socket.py", line 582, in readinto
    return self._sock.recv_into(b)
socket.timeout: timed out

I'm able to reproduce the failure on my Fedora 27 using two terminals:

(1) Run the test in a loop:
vstinner@apu$ ./python -m test -v test_ftplib -m test_check_hostname -F

(2) Stress the system, example:
vstinner@apu$ ./python -m test -j0 -r

When the system load becomes higher than 2 (I have 8 logical CPUs), test_check_hostname() fails.

New changeset 51500f37453bbcbc5f1dbc3c38d079c3c1efe5de by Victor Stinner in branch 'master':
bpo-32706: Skip test_ftplib.test_check_hostname() (#5422)
https://github.com/python/cpython/commit/51500f37453bbcbc5f1dbc3c38d079c3c1efe5de

Some tests still use asyncore to test TLS. Yes, that's old asyncore, not asyncio. I suggest that we replace asyncore with a threaded test server from test_ssl.

poplib is also affected, see #32753

Yep, I'm seeing those same failures in our internal build of 3.7.0b1.  I'll just disable the tests for now and nosy on this issue.

Ned, I'm going to rewrite part of the test infrastructure during beta phase. The ssl module now works according to specifications. When the client doesn't recognize a hostname, it aborts the TLS connection with a TLS ALERT message. The old asynchat test system cannot handle TLS connection abort correctly.

It's really just testing. No public APIs will be affected.

Let's get the changes into master first and stabilized there and then we can discuss the possibility of a 3.7 backport.

Christian Heimes: "Ned, I'm going to rewrite part of the test infrastructure during beta phase. (...)"

Any progress on rewriting these tests?

Since this is just an intermittent test failure and we have lived with it this long, I think it can wait for 3.7.1 at this point.  Downgrading to "critical".

Oh. I forgot about this change. The test is still skipped :-(

Christian: It seems like the test now pass on my Fedora 27. Is it time to enable the test again?

> Christian: It seems like the test now pass on my Fedora 27. Is it time to enable the test again?

Ignore my comment. I forgot that it's a race condition and I'm still able to get the failure using msg311097 scenario.

Ok, let's keep this permanent temporary fix (test skipped until someone finds a solution). I close the issue.