Add test upgrade StackLight. Minor changes

Change-Id: Ic863f65da4c36efd3bc5cb186e224d61cc7682ee
diff --git a/tcp_tests/managers/sl_manager.py b/tcp_tests/managers/sl_manager.py
index f65f524..1a97737 100644
--- a/tcp_tests/managers/sl_manager.py
+++ b/tcp_tests/managers/sl_manager.py
@@ -37,9 +37,8 @@
         super(SLManager, self).__init__(
             config=config, underlay=underlay)
 
-    def install(self, commands):
-        self.execute_commands(commands,
-                              label='Install SL services')
+    def install(self, commands, label='Install SL services'):
+        self.execute_commands(commands, label=label)
         self.__config.stack_light.sl_installed = True
         self.__config.stack_light.sl_vip_host = self.get_sl_vip()