Disable image-backed unit tests temporarily.

They are prone to breaking and leaving a mess on the test system.
They should be converted to use a vm to eliminate tainting (or being
tainted by) other tests.

tests/imagebackedtestcase.py

@@ -7,6 +7,7 @@
 from blivet.size import Size
 from blivet.flags import flags
 
+@unittest.skip("disabled until it can be converted to run in a vm")
 @unittest.skipUnless(os.environ.get("JENKINS_HOME"), "jenkins only test")
 @unittest.skipUnless(os.geteuid() == 0, "requires root access")
 class ImageBackedTestCase(unittest.TestCase):