Fix error message that says "delete" on the "activate" case.

bcl found this reviewing it.

Signed-off-by: Peter Jones <pjones@redhat.com>
Don't do unnecessary math.

bcl found this one too - we know len % 5 is 4, because it's tested a few
lines up.

Signed-off-by: Peter Jones <pjones@redhat.com>
Make the error case from make_boot_var() cleaner.

bcl thinks it looks better at the end, and I agree.

Signed-off-by: Peter Jones <pjones@redhat.com>