broadcast messages of new and deleted volumes

weed/pb/seaweed.proto

@@ -7,9 +7,7 @@ package master_pb;
 service Seaweed {
     rpc SendHeartbeat (stream Heartbeat) returns (stream HeartbeatResponse) {
     }
-    rpc KeepConnected (stream Empty) returns (stream Empty) {
-    }
-    rpc ListenForTopoChange (stream Empty) returns (stream VolumeLocation) {
+    rpc KeepConnected (stream ClientListenRequest) returns (stream VolumeLocation) {
     }
 }
 
@@ -58,8 +56,13 @@ message SuperBlockExtra {
     ErasureCoding erasure_coding = 1;
 }
 
+message ClientListenRequest {
+    string name = 1;
+}
+
 message VolumeLocation {
     string url = 1;
     string public_url = 2;
-    repeated uint32 vid = 3;
+    repeated uint32 new_vids = 3;
+    repeated uint32 deleted_vids = 4;
 }