Make InstanceInfoCache load base attributes

The InstanceInfoCache object is pretty bare-bones, previously needing
only the two main attributes. Since the virt/firewall module uses
the deleted flag, we need to load that now.

Related to blueprint compute-manager-objects
Related to blueprint virt-objects

Change-Id: I355a20b402c5581c1582cbe321c63bab58ee4815
Merge "Make InstanceInfoCache load base attributes"