run: explicitly specify format=raw for disk images

Not specifying a disk image file format leads to QEMU issuing a warning
and write-protecting block 0. This is seldom desirable:

```
WARNING: Image format was not specified for '/path/to/file' and probing guessed raw.
         Automatically detecting the format is dangerous for raw images, write operations on block 0 will be restricted.
         Specify the 'raw' format explicitly to remove the restrictions.
```

To squelch the warning, specify `format=raw` explicitly. This will be
made configurable in the next commit.

Signed-off-by: Ivan Shapovalov <intelfx@intelfx.name>

Author: intelfx

virtme/commands/run.py

@@ -1585,6 +1585,7 @@ def do_it() -> int:
                 "if=none",
                 f"id={driveid}",
                 f"file={disk.path}",
+                "format=raw",
             ]
             device_opts = [
                 arch.virtio_dev_type("blk"),
@@ -1616,6 +1617,7 @@ def do_it() -> int:
                 "if=none",
                 f"id={driveid}",
                 f"file={disk.path}",
+                "format=raw",
             ]
             device_opts = [
                 "scsi-hd",