Add replication of git from gerrit to git.o.o

Modify gerrit's git replication configuration so that it
pulls in from a list of replication targets defined in
puppet rather than individually added stanzas.

Pull the replicate_github variable from files, since it
is no longer required.

The replicate_local variable remains because it's used
in the apache configuration and for setup of the local
replication space for git.

Also add the cgit server to the list of servers.

Change-Id: I68de89bb216565f1754eb9b192bd437adcbf768b
Merge "Add replication of git from gerrit to git.o.o"