blueprint host-aggregates
blueprint host-aggregates

This is the first of a series of commits that add the host-aggregates capability,
as described on the blueprint page.

This commit, more precisely, introduces changes to the Nova model: model classes
related to aggregates have been added, as well as DB API methods to interact with
the model; a sqlalchemy migration script plus a bunch of tests are also part of
this changeset.

Commits that will follow are going to add:

- Extensions to OSAPI Admin, and related python_novaclient mappings
- Implementation of the XenAPI virt layer
- Integration of OSAPI and virt layer, via the compute_api
- smoketests
- openstack-manuals documentation

These commits will be pushed for review not necessarily in this exact order.

Change-Id: Iceb27609dc53bf4305c02d7cbc436fba4c4a7256

openstack/oslo.versionedobjects,citrix-openstack-build/oslo.versionedobjects