Add oslo.config compatibility attributes

In trying to get the OpenStack server projects to consume keystoneauth,
we ran in to the fact that they want to treat the things registered with
"register_conf_options" as oslo.config objects. It works fine that they
aren't - except that an oslo.config option has an attribute called
'deprecated_opts' while ours is called 'deprecated'. The same is true
of the other three attributes added.

Change-Id: I7d53c17d518b01946e091702a582648998c2ae17

keystoneauth1/loading/opts.py

@@ -88,6 +88,11 @@ class Opt(object):
         self.deprecated = [] if deprecated is None else deprecated
         self.default = default
         self.metavar = metavar
+        # These are for oslo.config compat
+        self.deprecated_opts = self.deprecated
+        self.deprecated_for_removal = []
+        self.sample_default = None
+        self.group = None
 
     def __repr__(self):
         return '<Opt: %s>' % self.name