replicate Gerrit repos to Jenkins slave gallium

gallium already has replicated repository under /var/lib/git which is a
different device than /srv/ where the jobs are doing the clone
operation.

/var/lib/git is hardcoded in too many place to let us do a migration so
to play it safe I am requesting to have a second replication setup under
/srv/ssd/gerrit just like lanthanum.

Once all jobs and scripts have been updated to use /srv/ssd/gerrit
instead of /var/lib/git, the replication 'inside-wmf' can be deleted.

Change-Id: I7428331e06ebeb08bb8ac3188ec745fa265ddf99
Merge "replicate Gerrit repos to Jenkins slave gallium" into production