tests: Add multiplextest

Add a test that exercises the multiplex system, as well
as the system to access parameters passed to the test
(self.params).

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado: Keep Pydev happy

Add some exceptions to the Eclipse Pydev linting system,
so those false negatives don't show.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>