Judging by the faulthandler traceback in the PowerLinux build:

Timeout (1:00:00)!
Thread 0x0000008074e46670 (most recent call first):
  File "/home/shager/cpython-buildarea/3.4.edelsohn-powerlinux-ppc64/build/Lib/test/test_cmd_line_script.py", line 192 in interactive_python
  File "/home/shager/cpython-buildarea/3.4.edelsohn-powerlinux-ppc64/build/Lib/contextlib.py", line 59 in __enter__
  File "/home/shager/cpython-buildarea/3.4.edelsohn-powerlinux-ppc64/build/Lib/test/test_cmd_line_script.py", line 205 in check_repl_stderr_flush
  File "/home/shager/cpython-buildarea/3.4.edelsohn-powerlinux-ppc64/build/Lib/test/test_cmd_line_script.py", line 220 in test_repl_stderr_flush
[snip]

... the test is actually stuck trying to read the interactive prompt from stderr:

            # Drain stderr until prompt
            while True:
                data = stderr.read(4)
                if data == b">>> ":
                    break
                stderr.readline()            <-- HERE