Bug#792547: Bug#789798: grub-installer: add option to _not_ install to UEFI boot order

[Ian Campbell]

Control: block 789798 by 792547

I've tested both of these patches (grub-installer [0] and grub2 [1]
together but the grub-installer one doesn't do much without the grub2
one, since it appears that the installation of the grub-* packages also
ends up running grub-install during installation.

Ian.

[0] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=789798#65
[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=792547#5