Switch to creating UEFI ESPs using loader.efi instead of boot1.efi.

Switch to creating UEFI ESPs using loader.efi instead of boot1.efi.
Cope for the fact that laoder.efi, not being boot1, doesn't read
/boot.config by setting boot_serial and force the serial console.

Also add sysctl so we can display the boot method.

Provide a variable, do_boot1_efi, if you want to use boot1 for
testing. But since it's transient, it's just a variable and not
available on the command line.