api: Implement bucket notification. (#2271)

* Implement basic S3 notifications through queues

Supports multiple queues and three basic queue types:

1. NilQueue -- messages don't get sent anywhere
2. LogQueue -- messages get logged
3. AmqpQueue -- messages are sent to an AMQP queue

* api: Implement bucket notification.

Supports two different queue types

- AMQP
- ElasticSearch.

* Add support for redis

xl-v1-bucket.go

@@ -207,6 +207,10 @@ func (xl xlObjects) listBuckets() (bucketsInfo []BucketInfo, err error) {
 				if !IsValidBucketName(volInfo.Name) {
 					continue
 				}
+				// Ignore the volume special bucket.
+				if volInfo.Name == minioMetaBucket {
+					continue
+				}
 				bucketsInfo = append(bucketsInfo, BucketInfo{
 					Name:    volInfo.Name,
 					Created: volInfo.Created,