Since the create_incomplete_consumers online data migration
was copied from nova to placement, and will eventually be
removed from nova (and the nova online data migration won't
help once the placement data is copied over to extracted placement
on upgrade anyway), this adds an upgrade check to make sure
operators completed that online data migration.
Normally we wouldn't add upgrade checks for online data migrations
which should get automatically run by deployment tools, but since
extracted placement is very new, it's nice to provide tooling to
let operators know they have not only properly migrated their
data to extracted placement but whether or not their upgrade
homework is done.
Change-Id: I7f3ba20153a4c1dc8f5b209024edb882fcb726ef
0f97cebedd