Use of capsys causes log access errors on unit test failures

[ca-johnson]

noticed in #203

When unit tests fail, there is an issue where log file is closed prior to test exiting.

Example error:

Message: 'p4 sync --parallel=threads=0 //...'
Arguments: ()
--- Logging error ---
Traceback (most recent call last):
  File "/Users/carl/.pyenv/versions/3.6.0/lib/python3.6/logging/__init__.py", line 989, in emit
    stream.write(msg)
ValueError: I/O operation on closed file.

Repro caused by removing one of the with exception blocks in a unit test (or adding one where an exception is not raised)

I was able to track this down to the use of capsys in test_server_fixture

If we remove such usage, the issue is resolved. However, it is quite convenient to print to stdout the server address.

Suggested solutions:

• Find a workaround to allow continued use of capsys
• Remove use of capsys, add to instructions in test_server_fixture to run pytest with a special flag to disable output capturing so you can still see the test server address printed to stdout