Make HostManager track NUMA usage

This patch adds tracking of NUMA usage in scheduler's HostManager class,
by adding it to the HostState, and making sure it gets updated along
with all the other usage data.

Change-Id: Id31c9a7fd54b918b3d38abb61b305cf7048a6a7d
Blueprint: virt-driver-numa-placement
Merge "Make HostManager track NUMA usage"