Master add clone command tests

Add tests of the CloneCommand implementation.

The tests fail on Windows because they are unable to remove 
the temporary directory after the test completes.  That is the 
pattern which was detected previously in JENKINS-19994.

More work is needed before the Jenkins JGit plugin closes 
all the files it opens.  These tests pass on Linux, and fail on
Windows with the message that the temp dir used for the
test cannot be deleted.