based on the outcome of spike OSP-21365 we have decided that the best way to remove the use of libguestfs in our product is to extend the default_ephemeral_format to include a new option hat disabled formatting the ephemeral disk.

currently, libguestfs is only used in two places file injection and ephemeral disk creation.
we do not support file injection in our product so by adding default_ephemeral_format=unformated upstream and then only supporting that in our product we can remove all dependency on libguestfs in the nova-compute container.