MB-11060:  use  git@github.com:couchbase/voltron.git

Change-Id: If8d2bcf579d898926c87f08ca4b4b597cb855067
Reviewed-on: http://review.couchbase.org/41664
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>