Check for extra files on unit test runs.

After running python unit tests, make sure there are no new
files in the repo that are not listed in .gitignore.  This
includes empty directories.

This will only print the result for now, later we can enforce
this by exiting with failure if there are new files.

Change-Id: I9501c3ee19d5289214976bc5e7cb58edb422e645
Reviewed-on: https://review.openstack.org/19966
Reviewed-by: Maru Newby <mnewby@internap.com>
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins