GOCBC-72: Use a larger channel for bulk op signalling.

We were encountering a situation where the bulk op execute's were
getting stuck waiting for room in the pipeline, but the pipeline
could not proceed because a previous op was blocking on the signal
channel which wasn't yet being read from.

Change-Id: I7bb01f759c61411a33bb659880ccaa17a777b174
Reviewed-on: http://review.couchbase.org/57124
Tested-by: Brett Lawson <brett19@gmail.com>
Reviewed-by: Mark Nunberg <mark.nunberg@couchbase.com>

bucket_multi.go

@@ -25,7 +25,10 @@ type BulkOp interface {
 func (b *Bucket) Do(ops []BulkOp) error {
 	timeoutTmr := gocbcore.AcquireTimer(time.Second * 10)
 
-	signal := make(chan BulkOp, 1)
+	// Make the channel big enough to hold all our ops in case
+	//   we get delayed inside execute (don't want to block the
+	//   individual op handlers when they dispatch their signal).
+	signal := make(chan BulkOp, len(ops))
 	for _, item := range ops {
 		item.execute(b, signal)
 	}