Always unset instance->wait when done waiting

Change-Id: I4b5b9ab8a0d910859e30875f1cae44d2a09d6347
Reviewed-on: http://review.couchbase.org/31740
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>