[sources] Simplify source's init method
Only call it when enabled instead of giving a boolean flag indicating whether it
is or not (which were not correctly considered).
.. _auth_module:
:mod:`cubicweb.pyramid.auth`
----------------------------
.. automodule:: cubicweb.pyramid.auth
.. autofunction:: includeme
.. autoclass:: UpdateLoginTimeAuthenticationPolicy
:show-inheritance:
:members: