generic.tests.cfg: Small fix for multi_queues_test

(1) Host_RHEL.6 and Host_RHEL.5 not support MQ, disable it.
(2) RHEL.6.6 guest is ready to support MQ now, so add this guest back.

Signed-off-by: Shuping Cui <scui@redhat.com>
Merge pull request #150 from spcui/multi_queues_test

generic.tests.cfg: Small fix for multi_queues_test