volume: add capability to change disk type when moving a volume

weed/shell/command_volume_copy.go

@@ -52,6 +52,6 @@ func (c *commandVolumeCopy) Do(args []string, commandEnv *CommandEnv, writer io.
 		return fmt.Errorf("source and target volume servers are the same!")
 	}
 
-	_, err = copyVolume(commandEnv.option.GrpcDialOption, volumeId, sourceVolumeServer, targetVolumeServer)
+	_, err = copyVolume(commandEnv.option.GrpcDialOption, volumeId, sourceVolumeServer, targetVolumeServer, "")
 	return
 }