FWaaS is using stateless ACL rules in OVN when OVN driver is used. That
means that traffic for both directions needs to be allowed explicitely
always.
This patch adjusts
fwaas.scenario.test_fwaas_v2.TestFWaaS_v2.test_icmp_reachability_scenarios
test so that in the 3rd step it allows ICMP traffic in both directions
and test is passing.
This patch also adds new config option `driver` in the `fwaas` group.
This option can be used to tell Tempest what FWaaS driver is used in the
deployment so that appropriate test path can be choosen.
Change-Id: I4f238300069df4777245bb64f83824ea36296cc7
c732e87acc