Add numa_topology column to the compute_node table

This patch adds the migration to add the numa_topology column to the
compute_node table. It also adds the field to the ORM model and the
Nova object class.

Change-Id: I4ca994662ed700a907f78aa04016b626fc351b25
Blueprint: virt-driver-numa-placement
Merge "Add numa_topology column to the compute_node table"