This PS unskips the last remaining git test in test_source which
had an unconditional unittests.skip() decorator applied to it.
The source_cleanup test now issues a warning if the repo path
isn't found and the associated test (passing in a bad path)
simply asserts that the warning was called.
This also adds a conditional skip to the git clone unit tests
in the event that the user doesn't have network connectivity.
Change-Id: Ic300c48a4e0c361e37ec15cd3675415f8170a817
bfff1f4ed3