mrtest: add_packages: Handle case when sudo/doas fails

Hi @ollieparanoid ,

here's fix for another open issue #10 (closed)

What now?> a
2 of 2 selected.
What now?> y
Selection confirmed
Extracting packages from artifacts archive...
Installing packages...
[sudo] password for user:
Sorry, try again.
[sudo] password for user:
Sorry, try again.
[sudo] password for user:
sudo: 3 incorrect password attempts
Failed to install packages!