For some reason we were only reading deleted instances when loading generic
fields and not things like flavor. That weird behavior isn't very helpful,
so this makes us always read deleted for that case. Some of the fields, like
tags, will short-circuit that and just immediately lazy-load an empty set.
But for anything else, we should allow reading that data if it's still there.
With this change, we are able to remove a specific read_deleted='yes' usage
from ComputeManager._destroy_evacuated_instances() which is handled with
the generic solution. TestEvacuateDeleteServerRestartOriginalCompute asserts
that the evacuate scenario is still fixed.
Related-Bug: #1794996
Related-Bug: #1745977
Change-Id: I8ec3a3a697e55941ee447d0b52d29785717e4bf0