Raise NotImplementedError in the base archivator

Use an exception for not implemented methods which is suitable to be
used in such cases.

Change-Id: Ibd3126d55ef8986ee431d61e76bfe89453891f67

octane/handlers/backup_restore/base.py

@@ -35,10 +35,10 @@ class Base(object):
         return name
 
     def backup(self):
-        raise NotImplemented
+        raise NotImplementedError
 
     def restore(self):
-        raise NotImplemented
+        raise NotImplementedError
 
     def pre_restore_check(self):
         pass