secure boot: signal security error back to the caller
secure boot: signal security error back to the caller

I needed a modification to gummiboot: it has to signal back to the
calling program that it had a security error so that the original loader
can ask the user to enrol the hash of the kernel for booting.

aaronp24/gummiboot,todorez/tummiboot,FrozenCow/gummiboot,trilean/gummiboot,trilean/gummiboot,android-ia/platform_external_gummiboot,liliang365/my_gummiboot,freedesktop-unofficial-mirror/gummiboot,todorez/gummiboot-multiboot2,karelzak/gummiboot,liliang365/my_gummiboot,FrozenCow/gummiboot,freedesktop-unofficial-mirror/gummiboot,todorez/tummiboot,karelzak/gummiboot,todorez/gummiboot-multiboot2,android-ia/platform_external_gummiboot,aaronp24/gummiboot,miguelinux/gummiboot2systemd-boot,miguelinux/gummiboot2systemd-boot