CBQE-0: rest_client implementation graceful failover

Change-Id: Ia9f2a6bdd5a6172e9f7efb0073e2ce76fbc6a5c6
Reviewed-on: http://review.couchbase.org/34620
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>