Static IP assignment, private network interface configuration, and floating IP address allocation

This introduces three things (with more detailed info in the commit messages):

* Handling of static IP addresses, so that one can assign a static private IP to an instance at the hypervisor level
* Handling of VM network interface configuration, so the above static IP can be configured statically at the instance level (except for the management interface, which is ignored)
* Allocation (and subsequent release) of floating IP addresses to an instance

Feedback is appreciated. :)