Decouple resources and preconditions in secgroup scenario

Handle secondary tenant checks based on CONF file only instead of using clients

Skip only cross-tenant test instead of whole class if secondary tenant is not
available

Change-Id: I9863ff840b9c5b18fa46826aab3fc107454dcc24
Merge "Decouple resources and preconditions in secgroup scenario"
Merge branch 'master' of https://github.com/openstack/tempest