I seem to be having this issue on CentOS 7.4 but running on x86_64 instead of ppc64le. I have attached an strace using version 4.17 (the lastest version from scl) created as follows:

strace -s 128 -e trace=%network -o trace ./python -m test -v test_socket -m test_sha256


== CPython 3.6.3 (default, Oct 13 2017, 11:16:36) [GCC 4.8.5 20150623 (Red Hat 4.8.5-16)]
== Linux-3.10.0-693.2.2.el7.x86_64-x86_64-with-centos-7.4.1708-Core little-endian
== cwd: /home/ryan/Downloads/Python-3.6.3/build/test_python_4140
== CPU count: 8
== encodings: locale=UTF-8, FS=utf-8
Run tests sequentially
0:00:00 load avg: 0.13 [1/1] test_socket
test_sha256 (test.test_socket.LinuxKernelCryptoAPI) ... ERROR

======================================================================
ERROR: test_sha256 (test.test_socket.LinuxKernelCryptoAPI)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/ryan/Downloads/Python-3.6.3/Lib/test/test_socket.py", line 5424, in test_sha256
    op.sendall(b"abc")
OSError: [Errno 126] Required key not available

----------------------------------------------------------------------
Ran 1 test in 0.001s

FAILED (errors=1)
test test_socket failed
test_socket failed

1 test failed:
    test_socket

Total duration: 39 ms
Tests result: FAILURE