Fix UserNotFound exception for expiring groups

Without this patch, if this exception is reached, it won't be properly
formed and will result in a log message like this:

  Failed to insert replacement values into translated message Could not
  find user: %(user_id)s. (Original: 'Could not find user:
  %(user_id)s.'): 'user_id'

This patch adds the right parameters to ensure the exception properly
logs the user ID and the translation doesn't fail.

Change-Id: I3229d9a237633cda8f6a25f396a75b8310757d9d

keystone/identity/shadow_backends/sql.py

@@ -230,7 +230,7 @@ class ShadowUsers(base.ShadowUsersDriverBase):
                 if not user:
                     # Note(knikolla): This shouldn't really ever happen, since
                     # this requires the user to already be logged in.
-                    raise exception.UserNotFound()
+                    raise exception.UserNotFound(user_id=user_id)
                 return user
 
         with sql.session_for_write() as session: