pipeline/assembler/qemu: rework partition table handling

Move to the new options format, allowing more flexible partition
tables. The pipeline changes, but the result should be the same.

This requires a yet-to-be-released version of osbuild.

Signed-off-by: Tom Gundersen <teg@jklm.no>

test/cases/openstack_local_boot.json

@@ -166,9 +166,20 @@
       "options": {
         "format": "qcow2",
         "filename": "image.qcow2",
+        "size": 3222274048,
         "ptuuid": "0x14fc63d2",
-        "root_fs_uuid": "76a22bf4-f153-4541-b6c7-0332c0dfaeac",
-        "size": 3222274048
+        "pttype": "mbr",
+        "partitions": [
+          {
+            "start": 2048,
+            "bootable": true,
+            "filesystem": {
+              "type": "ext4",
+              "uuid": "76a22bf4-f153-4541-b6c7-0332c0dfaeac",
+              "mountpoint": "/"
+            }
+          }
+        ]
       }
     }
   }