[FS#264] xen_domu images need change to grub.cfg to boot unattended

[LEDE Bugs]

The following task is now closed:

FS#264 - xen_domu images need change to grub.cfg to boot unattended
User who did this - Mathias Kresin (mkresin)

Reason for closing: Fixed
Additional comments about closing: https://git.lede-project.org/81e3c022e017be76d4f3eaf67cfd7ddba09e85be

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=264