Add the user id and project id of the user initiated the instance action to the notification

The instance action notifications contain the user id and the project id of the owner of the instance. However an instance action might be initiated by another user. It could be another user from the same project or can be an admin from the admin project. To be able to distinguish between the user who initiated the instance action from the user owning the instance we need to add two new fields to the instance action notifications, action_initiator_user and action_initiator_project (please bikeshed on the name). These new information can be filled from the context the instance action is running in.

The original request come over IRC: http://eavesdrop.openstack.org/irclogs/%23openstack-nova/%23openstack-nova.2018-01-11.log.html#t2018-01-11T10:12:16