CBLT-298:  change jenkins jobs to prepare_release_sgw_master, prepare_release_sgw_100

Change-Id: Iadc98a1ce3176bfa880ca97de3e2c4a337dc7142
Reviewed-on: http://review.couchbase.org/37874
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>