Comment 1 for bug 1704788

This was introduced in this change in Ocata:

https://review.openstack.org/#/c/349666/

There should have been a release note with that, and this part of the help text was wrong after that change:

"A custom scheduler driver. In this case, you will be responsible for
   creating and maintaining the entry point in your 'setup.cfg' file"

There was an older change made in Newton to stop allowing classloading of the scheduler driver and instead rely on stevedore:

https://review.openstack.org/#/c/254768/

But that meant you could still put your own scheduler driver "nova.scheduler.driver" entrypoint in setup.cfg to load a custom scheduler driver, which was then broken with the use of "choices" in https://review.openstack.org/#/c/349666/ for the config option - without warning or a deprecation period on custom scheduler driver entry points, so yeah, seems like a bug to at least communicate this better before removing it.

Note, however, that Nova is and has been for awhile removing the ability to load out of tree drivers and manager classes, so any fix here is likely to still deprecate the out of tree loading ability.