CBQE-2350: dcp multi-bucket tests

adding client auth support for multi bucket stream requests and sample
test case

Change-Id: I8b6e9f6f7cd4352d6bcf744f794621902ae7939b
Reviewed-on: http://review.couchbase.org/39966
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Tommie McAfee <tommie@couchbase.com>
Tested-by: Tommie McAfee <tommie@couchbase.com>