reset network should also re-inject updated network info

The compute manager has a mechanism for reseting a guest instance's networking. I originally intended for this functionality to be used to include any possibly altered network information by requesting it from network.

I see two possible ways of doing this, one is to add a new function which updates the network info in whatever way the virt drivers handle it. The other is to alter the reset_network function in the compute manager to get the instance's network info (which will come from network and be fresh) and pass it to an altered virt reset_network that accepts network info and handles it in the virt driver's way.

USE CASE:
I have an existing instance. I have decided to add a fixed ip to it. The guest (agent) needs to be aware of this ip and configure it.
I have an existing instance. I have decided to connect this instance to a new network which requires creating a new virtual interface with corresponding network infrastructure behind it, and then attaching it to a guest. The guest (agent) then needs to configure the interface.

I don't see this as being more than a week's work. It's little enough work that I was considering just making a bug for it.

I plan on doing the work in the next few days.