Do not assume users have names

This should be a safe assumption, but hughsaunders ran into a deployment
where a small subset of users (backed by AD) were configured with:

    [ldap]
    user_name_attribute = sAMAccountName

Where sAMAccountName happens to be an optional attribute in some LDAP
systems, resulting in those users not having "name" attributes available
via Keystone's API.

closes-bug: 1431942

Change-Id: Ic69e571c71fd462c65791800eaaa474917dec2ef

playbooks/library/keystone

@@ -461,7 +461,7 @@ class ManageKeystone(object):
         :param name: ``str``  Name of the user.
         """
         for entry in self.keystone.users.list():
-            if entry.name == name:
+            if getattr(entry, 'name', None) == name:
                 return entry
         else:
             return None