Bogus power state when a node is in maintenance

[Dmitry Tantsur]

When we move nodes to maintenance mode for reasons not related to power fault, we keep the last power state in the database. As we don't sync power states, it never gets updated, no matter what happens to the node. It can cause confusion, as described in https://bugzilla.redhat.com/show_bug.cgi?id=1433416 when operators believe that node is powered off, while it's actually on.

We can either set power state to None to indicate "I don't know" or sync power state without enforcing it. The latter can put unnecessary load on the BMC, so I think we should do the former.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/460523

[OpenStack Infra (hudson-openstack)]

Change abandoned by Dmitry Tantsur (<email address hidden>) on branch: master
Review: https://review.openstack.org/460523
Reason: Unfortunately, I don't have time to figure out this. Anyone is free to take over.