Open Stack

Just a heads up that this recently merged code is wrong:

https://review.openstack.org/#/c/192760/14/nova/tests/unit/db/test_migrations.py,cm

and here it is failing tests on my local env, as it does on my CI, as 
would be expected, there's a lot more if I keep it running:

http://paste.openstack.org/show/412236/

However, utterly weirdly, all those tests *pass* with the same versions 
of everything in the gate:

http://paste.openstack.org/show/412236/


I have no idea why this is.  This might be on the oslo.db side within 
the test_migrations logic, not really sure.    If someone feels like 
digging in, that would be great.

The failure occurs with both Alembic 0.7.7 and Alembic 0.8 as yet 
unreleased.  I have a feeling that releasing Alembic 0.8 may or may not 
bump this failure to be more widespread, just because of its apparent 
heisenbuggy nature, and I'm really hoping to release 0.8 next week.  It 
was supposed to be this week but I got sidetracked.