Move from old drive expressions to newer blockdev expressions

This catches up with the Qemu command line which has deprecated
the drive option for quite a while now.

tp_folder/configs/guest-base.cfg

@@ -439,5 +439,5 @@ remove_set = minimal
 
 
 ## Miscellaneous parameters
-# Custom environment path for the vms
-qemu_force_use_drive_expression = yes
+# Provide auto-readonly configuration for block devices
+image_auto_readonly = yes