Fix activating and deactivating a hook (esp the ticket-hook)
Previously the ticket-hook would raise a 404 error itself, making
the code in the hook controller section by-passed and thus not allowing
to rollback the session, practically practically rendering pagure stuck
on a DB error (especially with RDBMS such as sqlite).
With this commit, the ticket-hook now raises an exception that the
controller catches and process as desired (rollback the DB session, raise
the corresponding http error).
This fix came with a few other changes found while debugging this issue,
such as the session not being rollbacked for other exceptions.
Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>