The AMD SEV support recently introduced to nova[0] depends on certain
metadata properties for flavors and images which were either missing
or only partially covered by existing glance metadata, so fill the
missing gaps:
- Add the hw:mem_encryption flavor extra spec and corresponding
hw_mem_encryption image property.
- hw_firmware_type has been supported by nova for quite a while,
so register it as an official metadata property.
- Add hw_cdrom_bus which was missing as per
https://bugs.launchpad.net/glance/+bug/1808868. This shares
values with hw_disk_bus, so document that too.
[0] https://docs.openstack.org/nova/latest/admin/configuration/hypervisor-kvm.html#amd-sev-secure-encrypted-virtualization
Closes-Bug: 1808868
Change-Id: I8116565ad0326d0125b320d840d787edcb086aa9