grub wrapper: skip if using boot-tool but also booted via EFI

grub wrapper: skip if using boot-tool but also booted via EFI

From Fabians feedback:
> this could have another guard for whether the system is even booted
> with grub as if the system was booted using EFI, re-initing all
> ESPs is just busy-work

So skip if proxmox-boot-tool and booted with EFI, as then GRUB is out
of the picture anyway.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>