If there is a non-zero number of arguments, run_tests.sh now
passes through the arguments to `manage.py test`, skipping the
default horizon/openstack_dashboard suites.
The correct settings module is chosen based on the first module
given in the argument. E.g., horizon.test.tests.tables chooses
the horizon.test.settings module.
Change-Id: I5321e87bec6831fb7574e045a82de06086b1d0d0