Compute Service

Now that we have a `block` service for virtual machine volumes and the ability to upload cloud images - we can now create the `compute` service on which the KVM hosts run their instances.

Requirements:
- Need to be able to create logical volumes
- Need to be able to download images to the block service and burn them into volumes
- Need to be able to expose logical volumes to compute hosts via ISCSI
- Need to be able to optionally run a block service on a compute service and use its volumes instead of ISCSI
- Need to be able to create a virtual machine
- Need to be able to use an existing network bridge
- Need to be able to connect to block service via ISCSI
- Need to be able to attach logical volume to instance via ISCSI