feat(vm_image_util): CloudStack support

Provide initial support for CloudStack.
CloudStack supports multiple hypervisors (XenServer, VMware and KVM) each using different disk format (VHD, OVA and QCOW2). AFAIK the XenServer is by far the most popular which is also the one I'm using for testing these changes, hence building the VHD image. Other installations which use different hypervisors may use the raw image and convert it to their desired format, at least that was my original reasoning.

If you prefer to build only VHD image, I'm happy to drop the raw one. Alternatively I can also add a build target for the QCOW2 and VMDK images if you want to support all hypervisors out-of-the-box.