Raise NotImplementedError instead of NotImplemented

NotImplementedError is the name of the exception
(https://docs.python.org/2/library/exceptions.html).
NotImplemented is the name of a constant
(https://docs.python.org/2/library/constants.html).

>>> raise NotImplemented()
Traceback (most recent call last):
  File "<pyshell#31>", line 1, in <module>
    raise NotImplemented()
TypeError: 'NotImplementedType' object is not callable
>>> raise NotImplementedError()
Traceback (most recent call last):
  File "<pyshell#32>", line 1, in <module>
    raise NotImplementedError()
NotImplementedError

This patch fix it.

Change-Id: Ia8bf7d75cd7f70e503b9669fc60ea9d89642489b
Closes-Bug: #1339855

fuelclient/commands/base.py

@@ -65,11 +65,11 @@ class BaseCommand(command.Command):
 
     @property
     def supported_file_formats(self):
-        raise NotImplemented()
+        raise NotImplementedError()
 
     @property
     def allowed_attr_types(self):
-        raise NotImplemented()
+        raise NotImplementedError()
 
 
 @six.add_metaclass(abc.ABCMeta)