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

object-utils.go

@@ -46,6 +46,10 @@ var isIPAddress = regexp.MustCompile(`^(\d+\.){3}\d+$`)
 // and periods, but must begin and end with a lowercase letter or a number.
 // See: http://docs.aws.amazon.com/AmazonS3/latest/dev/BucketRestrictions.html
 func IsValidBucketName(bucket string) bool {
+	// Special case when bucket is equal to 'metaBucket'.
+	if bucket == minioMetaBucket {
+		return true
+	}
 	if len(bucket) < 3 || len(bucket) > 63 {
 		return false
 	}