restart seriesly instance

-- get rid of scripts/sgw_clean_seriesly.sh
-- restart seriesly
-- start samplers after gateload
-- get rid of extra sleep

Change-Id: Ie5c92bf7f048c46ae2f28ecbe8cc278e090a5df5
Reviewed-on: http://review.couchbase.org/36943
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Li Yang <lichenyang2@gmail.com>