[RFE] iRMC OOB rescue mode support

[Vladyslav Drok]

This proposes to support OOB rescue mode by booting rescue image from
virtual media.
Supporting OOB rescue mode provides customer with the same network
configuration as costumer's production environment which is booted from
Cinder [1] in customer's tenant network.

If rescue mode booted from rescue network using Pluggable network
providers [2], IB rescue mode provides customer with NOT same network
configuration as costumer's production environment.
This would cause another problem when customer investigated problem in
their production environment.

Therefor it is better to support not only IB rescue mode [3], but also OOB
rescue mode.

[1] https://bugs.launchpad.net/ironic/+bug/1526231
[2] https://bugs.launchpad.net/ironic/+bug/1526401
[3] https://bugs.launchpad.net/ironic/+bug/1526449

- Nov 9th, 2015, Naohirot:
Overall idea can be found in the following presentation slides P.56 - P.58.

"Ironic Towards Truly Open and Reliable, Eventually for Mission Critical"
 http://www.slideshare.net/naohirot/ironic-towards-truly-open-and-reliable-eventually-for-mission-critical
 https://www.youtube.com/watch?v=MpSqDA3jo0I

[Jim Rollenhagen (jim-rollenhagen)]

spec is here: https://review.openstack.org/250648

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Julia Kreger <email address hidden>" on branch: master
Review: https://review.opendev.org/c/openstack/ironic-specs/+/250648
Reason: Abandoning due to inactivity. In essence, this proposes virtual media based rescue, however rescue over virutal media should already be a thing, boot interface and driver permitting. The iRMC driver does have some virtual media support, so in theory it *should* just work, but as a community

[Jay Faulkner (jason-oldos)]

Unsure the status of this feature, but the bug is very dusty. If we want to continue to implement this, we should address it as a new RFE.

[Julia Kreger (juliaashleykreger)]

That being said, I suspect this should just work, and would treat this not working today as a bug instead.