Report remote mirror URL change to stdout rather than failing test

The getHeadRev test methods generally work on a local mirror which is
unchanging.  However, one of the important use cases requires a check
of a remote mirror.  That remote mirror may have changed since the
local mirror was created.  If that change happens, then the tests
previously would fail.

Rather than fail the tests, write a message to stdout that the tests
is not being performed.  If the git-client-plugin tests in that file
switch to JUnit 4 in the future, then we could use a conditional
ignore to mark the test as ignored in the JUnit XML output, rather
than hiding the "ignore" in the stdout of the test.