[Libguestfs] [PATCH 0/2] builder: Add test that a serial console is set up for guest templates we supply.

The first of two sets of patches. This checks that the templates we supply have the serial console enabled, or in two cases, that the serial console can be enabled by fiddling with some grub config. The second set of patches (to follow) will test that the --password and --root-password options work. This implementation of this is quite complex. Rich.