Return the correct user from the last update resource

Review Request #9709 — Created April 25, 2018 and submitted — Latest diff uploaded

Information

Review Board
release-3.0.x
77756b5...

Reviewers

A while back we started recording who published review requests in the
ChangeDescription so that re-assigned review requests showed proper
history (instead of just showing the new author doing everything).
This patch updates the ReviewRequestLastUpdateResource to take this
information into account.

As a part of this change, ReviewRequest.get_last_activity has been
deprecated in favour of a new method,
ReviewRequest.get_last_activity_info, which returns a dict of
information, including the relevant ChangeDescription, which can be
used to determine the author of the update.

Additionally, unit tests have been added to cover the last update
resource's behaviour.

Ran unit tests.