feat(image_to_vm): Switch to qcow2 as default qemu disk format.

We only really need raw images for dd'ing to block devices and this
format has been requested for some cases so lets just use it!
fix(image_to_vm): Replace qemu's config file with a script.

The recommended command using the config file was triggering a massive
memory leak in qemu because it was adding both the default virtual
hardware nic as well as the virtio nic. This could be worked around by
adding something like -net none or moving all the -net commands from the
file to the command line but eh. Clearly qemu config files are used and
tested by nobody else so lets just use a trusty script instead.
feat(image_to_vm): Add openstack image, uses oem-ami and qcow2 format.
Merge pull request #77 from marineam/qcow2

Qemu, Qcow2, and Openstack