Add SEV-related extra spec and image properties

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

etc/metadefs/compute-libvirt-image.json

@@ -10,6 +10,22 @@
         }
     ],
     "properties": {
+        "hw_cdrom_bus": {
+            "title": "CD-ROM Bus",
+            "description": "Specifies the type of disk controller to attach CD-ROM devices to.",
+            "type": "string",
+            "enum": [
+                "scsi",
+                "virtio",
+                "uml",
+                "xen",
+                "ide",
+                "usb",
+                "fdc",
+                "sata",
+                "lxc"
+            ]
+        },
         "hw_disk_bus": {
             "title": "Disk Bus",
             "description": "Specifies the type of disk controller to attach disk devices to.",
@@ -22,7 +38,17 @@
                 "ide",
                 "usb",
                 "fdc",
-                "sata"
+                "sata",
+                "lxc"
+            ]
+        },
+        "hw_firmware_type": {
+            "title": "Firmware Type",
+            "description": "Specifies whether the image should be booted with a legacy BIOS or with UEFI.",
+            "type": "string",
+            "enum": [
+                "bios",
+                "uefi"
             ]
         },
         "hw_rng_model": {

etc/metadefs/compute-libvirt.json

@@ -26,6 +26,12 @@
             "description": "If true, enables the BIOS bootmenu. In cases where both the image metadata and Extra Spec are set, the Extra Spec setting is used. This allows for flexibility in setting/overriding the default behavior as needed.",
             "type": "string",
             "enum": ["true", "false"]
+        },
+        "mem_encryption": {
+            "title": "Hardware Memory Encryption",
+            "description": "Enables encryption of guest memory at the hardware level, if there are compute hosts available which support this. See https://docs.openstack.org/nova/latest/admin/configuration/hypervisor-kvm.html#amd-sev-secure-encrypted-virtualization for details.",
+            "type": "string",
+            "enum": ["true", "false"]
         }
     },
     "objects": []