Due to the deprecation of the self.skip(), the availability of the skip
decorators and the new CANCEL status, some internal improvements are
important to keep our behaviour sane and our own code sound and clean.

- The test.SkipTest class was renamed to test.MockingTest to be even more
  generic, intending to be overridden by sub-classes that make the test
  to end both with SKIP or CANCEL status. To keep it generic,
  test.MockingTest class will not SKIP the test if used directly anymore.

- The test.TimeOutSkipTest and test.ReplaySkipTest classes now are using
  the skip decorators instead of raising an exception in setUp(), since
  'skipping' the test means 'don't execute anything', not even the
  setUp().

- The test.DryRunTest class, which is expected to log itself in setUp()
  and then abort the test execution, is now using self.cancel() (instead
  of raising a SKIP exception), being now compliant with the concept
  that a SKIP test cannot execute anything.

- Selftests were adjusted accordingly.
Signed-off-by: NAmador Pahim <apahim@redhat.com>