Update git frontend regex to support more nodes

We are going to round robin multiple git.openstack.org frontends. Before
we build new nodes to do that we need to update the site.pp to properlly
configure new nodes with these names.

New name format will be git-frontendXX.openstack.org.

Change-Id: Id7f9405909c91e457270687592948456db3aa420
Merge "Update git frontend regex to support more nodes"