lcbio: free resources upon lcbio_cancel()

Don't wait for the next event loop iteration, otherwise we might end up
leaving events/sockets in scope after a call to lcb_destroy()

Change-Id: Id4f37417179d66a4286e03ddee562a7579c01974
Reviewed-on: http://review.couchbase.org/38100
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>