entropy.client.mirrors.StatusInterface: add two new methods.

Add set_working_mirror and add_failing_working_mirror methods with
the aim of increasing the usefulness of the class.

libraries/entropy/client/mirrors.py

@@ -23,6 +23,7 @@
 class StatusInterface(dict):
 
     def __init__(self):
+        self.__last_mirrorname = None
         dict.__init__(self)
 
     def add_failing_mirror(self, mirrorname, increment = 1):
@@ -36,3 +37,14 @@ class StatusInterface(dict):
 
     def set_failing_mirror_status(self, mirrorname, value):
         self[mirrorname] = value
+
+    def set_working_mirror(self, mirrorname):
+        self.__last_mirrorname = mirrorname
+
+    def add_failing_working_mirror(self, value):
+        if self.__last_mirrorname:
+            self.add_failing_mirror(self.__last_mirrorname, value)
+
+    def clear(self):
+        self.__last_mirrorname = None
+        return dict.clear(self)