Use disk optional configuration in qemu vm

If the optional disk properties are specified, use them in the qemu
command. We will use this to debug the random kernel panics on github
actions.

This can be added later to vfkit and krunkit if needed.

vmnet/vm.py

@@ -168,7 +168,7 @@ def qemu_command(self):
             raise ValueError("fd or socket required")
         qemu = QEMU_CONFIG[platform.machine()]
         firmware = qemu_firmware(qemu["arch"])
-        return [
+        cmd = [
             self.driver_command or f"qemu-system-{qemu['arch']}",
             "-name",
             self.vm_name,
@@ -202,6 +202,16 @@ def qemu_command(self):
             "-nodefaults",
         ]
 
+        # Optinal arguments
+
+        if "kernel" in self.disk:
+            cmd.extend(["-kernel", self.disk["kernel"]])
+        if "kernel_cmdline" in self.disk:
+            cmd.extend(["-append", self.disk["kernel_cmdline"]])
+        if "initrd" in self.disk:
+            cmd.extend(["-initrd", self.disk["initrd"]])
+
+        return cmd
 
 def qemu_firmware(arch):
     """