Permit specifying ovs bridge mappings too.
Permit specifying ovs bridge mappings too.

Another minor change to get a fully automated ci-overcloud deployment.

It's a shame this is all environment variable based - we'll have to
circle back and make this much nicer!

Change-Id: I5715a0ad6931c05dc10093c9abd5ecdb908e8246

rdo-management/tripleo,rdo-management/tripleo