Ignore the existance of /sys/firmware/efi if we are inside a chroot
Commit 8a81a537 broke the use-case of running flash-kernel inside a chroot to prepare a system image for another machine. If the machine outside the chroot has /sys/firmware/efi and bind-mounts sysfs into the chroot then flash-kernel will wrongly exit early. Thus, in this commit we additionally check if we are inside a chroot and only check /sys/firmware/efi if we are not.
Edited by Johannes Schauer Marin Rodrigues