CBQE-1151: distribute memcached requests

Retrieve active nodes from cache and randomly rotate which one does kv tasks.  previous implementations would only use the COUCHBASE_IP port

Change-Id: I089a2e7d011fb561efc4d8a40b4598bcae1f141a
Reviewed-on: http://review.couchbase.org/25293
Reviewed-by: Ketaki Gangal <ketakigangal@gmail.com>
Reviewed-by: Tommie McAfee <tommie@couchbase.com>
Tested-by: Tommie McAfee <tommie@couchbase.com>