1. Fixes the url for user update methods to reflect extension status,
e.g. 'users/{user_id}/tenant' to 'users/{user_id}/OS-KSADM/tenant',
as per Keystone API.
2. Fixes the update_user method, as it expects a POST instead of PUT.
Change-Id: I045ca7650b2ef8969af695900da1b4f62d4da6bd