Skip stateless SG related tests for backends which don't support it

Currently stateless SGs are supported by ML2/OVN backend and by backends
which uses iptables based firewall driver.
It's not supported e.g. by ML2/OVS with 'openvswitch' fw driver thus
those tests should be skipped in case of that backend driver.

Change-Id: I9fa572c3b7eda96706caa2ba1a181de475357804
1 file changed