doc: Rebuild vs. Evacuate (and other move-ish ops)

[Eric Fried]

Following discussion on IRC [1], it would be nice to have a contributor document describing the differences among the various move-ish operations -- for purposes of this bug, just rebuild and evacuate -- in terms of what happens to their allocations, images, UUIDs (instance vs migration), hosts (dest same/different from src), etc.

[1] http://eavesdrop.openstack.org/irclogs/%23openstack-nova/%23openstack-nova.2019-09-10.log.html#t2019-09-10T13:31:17

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/683245

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/683245
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=ddd7273ac35e4ff6c80853172338555039b368cc
Submitter: Zuul
Branch: master

commit ddd7273ac35e4ff6c80853172338555039b368cc
Author: Matt Riedemann <email address hidden>
Date: Thu Sep 19 17:55:19 2019 -0400

    Add evacuate vs rebuild contributor doc

    People often get confused about the differences between
    evacuate and rebuild operations, especially since the
    conductor and compute methods are both called "rebuild_instance".
    This change adds a contributor document which explains some
    of the high and low level differences between the two operations.

    Change-Id: I146fbc65237c4729ce3c28a4614589ba085dfce0
    Closes-Bug: #1843439

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/nova 20.0.0.0rc1 release candidate.