Add logging to test_supervisord_concurrency

This turned out to be very useful when debugging test failures I was
getting while working on PR #96.

nosetests has built-in support for capturing log output and printing it
(pytest can also do this if you `pip install pytest-capturelog`).
Merge pull request #97 from msabramo/test_export_supervisord__log_generated_contents

Add logging to test_supervisord_concurrency