CBST-8: set password for workload against sasl bucket

Change-Id: Ic9a3be38bbf596e1940c344808e5329367f89674
Reviewed-on: http://review.couchbase.org/28484
Reviewed-by: Tommie McAfee <tommie@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>