utils.unittest_suite: Remove the firewalld add unittest from short set

This unittest requires python APIs not available in python
2.4, and would be better to be executed in a full run, rather
than a short run.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Merge pull request #778 from autotest/remove-fwall-unittest-default-set

utils.unittest_suite: Remove the firewalld add unittest from short set