Call error callback on connection failure

Change-Id: I9eb82a6075c202a5d1100648a5e0cecd974d43aa
Reviewed-on: http://review.couchbase.org/28634
Reviewed-by: Brett Lawson <brett19@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>