astakos: Use bulk_create to speed up commissions

Update holdings and create provisions and log in bulk when issuing or
resolving commissions to speed up the operation,
astakos: update action logic

The following changes are made to the way actions are validated:

* accept: Accept only unmoderated or rejected users.
* deactivate: Deactivate only moderated users. This includes inactive
  users, solely for the purpose of changing their deactivation reason.
* send_verification_mail: Renew verification code and send it only to
  users with unverified mail.
astakos: Update user logic tests

Update tests according to the changes in activation_backends.py

closes grnet/synnefo#164
pithos: Add missing index

Add index on column 'node' of the ''versions' table.

closes grnet/synnefo#161