[nova] The race for 2.76

There are several compute API microversion changes that are conflicting and will be fighting for 2.76, but I think we're trying to prioritize this one [1] for the ironic power sync external event handling since (1) Surya is going to be on vacation soon, (2) there is an ironic change that depends on it which has had review [2] and (3) the nova change has had quite a bit of review already. As such I think others waiting to rebase from 2.75 to 2.76 should probably hold off until [1] is approved which should happen today or tomorrow. [1] https://review.opendev.org/#/c/645611/ [2] https://review.opendev.org/#/c/664842/ -- Thanks, Matt