Make user sync-gateway is really working before proceed to run sgw_test_info.sh and gateload

Change-Id: I1496aa7fce43a9b4b9ec670b0e02e545153f37a6
Reviewed-on: http://review.couchbase.org/37023
Reviewed-by: Li Yang <lichenyang2@gmail.com>
Tested-by: buildbot <build@couchbase.com>