txcouchbase: Invoke ready_w() on connection loss

Change-Id: I198343787de6d34b6d5caa3f048633f69100f64e
Reviewed-on: http://review.couchbase.org/32927
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>