Bug#1016737: Loop in POST when using --removable option in grub-install

[Pascal Hambourg]

I wrote:
> 
> I observe the same behaviour on my laptop.

And on another x86 desktop PC too. When loaded from the removable media 
path (/EFI/BOOT/BOOTX64.EFI), shim loads fbx64.efi which reboots the 
system if it did not find any BOOTX64.CSV file in /EFI/BOOT, as expected 
on removable media.

Here is the console output after setting FALLBACK_VERBOSE with

  mokutil --set-fallback-verbosity true

efi_main: System BootOrder not found.  Initializing defaults.
efi_main: tpm not present, starting the first image
Verbose enabled, sleeping for 500000 mseconds... Press the Pause key now 
to hold for longer.
Reset System
Verbose enabled, sleeping for 500000 mseconds... Press the Pause key now 
to hold for longer.

> My workaround is to remove EFI/BOOT/fbx64.efi from the EFI partition.
> IMO --removable should not install this file.

This is confirmed in the shim source package.

- In README.fallback:
When you boot removable media, it'll be in \EFI\BOOT , but fallback.efi
won't be there, so it goes ahead and boots the normal bootloader
(grubx64.efi).

- In shim.c:
	/* Do not print the error here - this is an acceptable case
	 * for removable media, where we genuinely don't want
	 * fallback.efi to exist.

Also fbx64.efi is not present in the EFI partition of Debian 
installation images.