This makes the evacuate process leave a record in the database about the
evacuation, and from what host it was being performed. Now, the compute
manager will use that breadcrumb trail to decide whether it should delete
locally-running instances, instead of just the hostname mismatch.
Since this does a query by migration_type, I added a unit test to the
test_db_api module to prove this actually works.
DocImpact: Deprecates the workarounds/destroy_after_evacuate config option
Related to blueprint robustify-evacuation
Closes-Bug: #1471887
Change-Id: I972c224dfb954a9f06e221c9235ee6e4889c2619
d9c696acf8