Some bootloader e.g grub supports graphics, text and also
serial consoles to hand over the output of the bootloader
menu. With this patch we allow to customize the console
used by the bootloader. So far only grub makes use of the
new attribute
<type ... bootloader_console="serial|console|gfxterm"/>
This references Trello:
https://trello.com/c/q9EhNKKV/155-support-for-grub2-serial-console
nose is no longer maintained, thus we have to move to another
testing system. This commit updates the tox setup and all tests
to use pytest instead of nose.
