On systems where the grub-pc package is not available (e.g. ARM),
dpkg-query will have an exit status of 1. Handle the error that is
raised in this case.
Tests:
- Added unit tests for storage._diagnose_grub_configured.
- Tested on Raspberry Pi 4.
Closes: #2441
Signed-off-by: James Valleroy <jvalleroy@mailbox.org>
Reviewed-by: Sunil Mohan Adapa <sunil@medhas.org>