Generalize 'object_url' to take extra arguments

I used *args so that it would be backwards-compatible with previous usage.
The only difference, and it's minor, is that now all arguments are
urllib-quoted.  Tested with two- and three- argument calls.

Quoting gsilvis (2014-06-27 23:26:57)
> In haas/cli.py:
> > @@ -60,14 +60,14 @@ def user_delete(username):
> >  @cmd
> >  def group_add_user(group, user):
> >      """Add <user> to <group>."""
> > -    url = object_url('group', group) + '/add_user'
> > +    url = object_url('group', group, 'add_user')
> 
>    You're right---it does change the meaning of the name. I think that,
>    until we get all of the API functions merged, we don't want to try
>    changing that name, because everyone will be using it as is, though.

Sure. Put a comment in as a TODO though.