Add support for evictionPolicy and bucket priority in system tests

Change-Id: I63379465e6178711562d1c1a8369104ccae089b9
Reviewed-on: http://review.couchbase.org/36751
Reviewed-by: Tommie McAfee <tommie@couchbase.com>
Tested-by: Aruna Piravi <aruna@couchbase.com>