avoid repeated grpc connection creation

fix https://github.com/chrislusf/seaweedfs/issues/1277

weed/pb/grpc_client_server.go

@@ -86,13 +86,15 @@ func WithCachedGrpcClient(fn func(*grpc.ClientConn) error, address string, opts
 		err := fn(existingConnection)
 		if err != nil {
 			grpcClientsLock.Lock()
-			delete(grpcClients, address)
+			// delete(grpcClients, address)
 			grpcClientsLock.Unlock()
-			existingConnection.Close()
+			// println("closing existing connection to", existingConnection.Target())
+			// existingConnection.Close()
 		}
 		return err
 	}
 
+	println(" dialing to", address, "...")
 	grpcConnection, err := GrpcDial(context.Background(), address, opts...)
 	if err != nil {
 		grpcClientsLock.Unlock()
@@ -105,9 +107,10 @@ func WithCachedGrpcClient(fn func(*grpc.ClientConn) error, address string, opts
 	err = fn(grpcConnection)
 	if err != nil {
 		grpcClientsLock.Lock()
-		delete(grpcClients, address)
+		// delete(grpcClients, address)
 		grpcClientsLock.Unlock()
-		grpcConnection.Close()
+		// println("closing created new connection to", grpcConnection.Target())
+		// grpcConnection.Close()
 	}
 
 	return err

weed/wdclient/masterclient.go

@@ -121,6 +121,9 @@ func (mc *MasterClient) tryConnectToMaster(master string) (nextHintedLeader stri
 }
 
 func (mc *MasterClient) WithClient(fn func(client master_pb.SeaweedClient) error) error {
+	for mc.currentMaster == "" {
+		time.Sleep(3 * time.Second)
+	}
 	return pb.WithMasterClient(mc.currentMaster, mc.grpcDialOption, func(client master_pb.SeaweedClient) error {
 		return fn(client)
 	})