[Newton] Nova notifications do not show the user which initiates the event.

[Yusuf Kanchwala]

Description
===========
Nova event notification does not show the actual user who initiated the event, instead show the owner of the VM.

Steps to reproduce
==================
1. Create a tenant "test-tenant".
2. Create two users; an admin "test-admin" and a SSO user "test-user"
3. Create a VM from "test-user"
4. Reboot the VM created in #3 from "test-admin"

Event notification show "test-user" in the events. It should rather show "test-user".

This is because while generating the event notification payload, information from instance is used instead of context information.

Code wise, in this line
https://github.com/openstack/nova/blob/808d36475103e373f1deb3344b6829ce68d6cdd5/nova/notifications/base.py#L432

Here we use:
user_id=instance.user_id

Should'nt we use, user that has come from context, something like
user_id=context.user_id

[Balazs Gibizer (balazs-gibizer)]

Based on comment above the linked code it is intentional to send the user id and project id of the _owner_ of the instance. Still I understand the need to know which user initiated the reboot action. Therefore I opened a blueprint to do this as a new addition to the versioned instance action notifications https://blueprints.launchpad.net/nova/+spec/add-action-initiator-to-instance-action-notifications