Make virt/firewall use objects for Security Groups and Rules

This makes the virt/firewall module use SecurityGroup and
SecurityGroupRule objects instead of relying on virtapi and
conductor for these operations.

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

Change-Id: I39cb9422cb15e6222f5009f64706f1528035f42d
Merge "Make virt/firewall use objects for Security Groups and Rules"