Skip CMD_GET_CLUSTER_CONFIG on server failout

Change-Id: I70e71bfad4f65f0c038473187ab31ad6035b6a10
Reviewed-on: http://review.couchbase.org/30884
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>