Peer RPCs for bucket notifications (#2877)

* Implements a Peer RPC router that sends info to all Minio servers in the cluster.
* Bucket notifications are propagated to all nodes via this RPC router.
* Bucket listener configuration is persisted to separate object layer
  file (`listener.json`) and peer RPCs are used to communicate changes
  throughout the cluster.
* When events are generated, RPC calls to send them to other servers
  where bucket listeners may be connected is implemented.
* Some bucket notification tests are now disabled as they cannot work in
  the new design.
* Minor fix in `funcFromPC` to use `path.Join`

cmd/server-main.go

@@ -386,6 +386,12 @@ func serverMain(c *cli.Context) {
 	globalObjectAPI = newObject
 	globalObjLayerMutex.Unlock()
 
+	// Initialize local server address
+	globalMinioAddr = getLocalAddress(srvConfig)
+
+	// Initialize S3 Peers inter-node communication
+	initGlobalS3Peers(disks)
+
 	// Initialize a new event notifier.
 	err = initEventNotifier(newObjectLayerFn())
 	fatalIf(err, "Unable to initialize event notification.")