Convert to a more modern form of openstack-common.conf

One module per line is the new hotness. I've also sorted the
modules alphabetically. There are no changes to your imports, but
this makes it easier for oslo maintainers to keep your imports up
to date.

Change-Id: I6e9ae5d8b953b81014bd60cc842af33c6af58b61
Nova Aggregate wrapper to manage host allocation pools