Don't call EPERM "not found" when deleting variables.

Signed-off-by: Peter Jones <pjones@redhat.com>
Produce a slightly more succinct error when we get -EPERM on the disk.

Because one error message is enough.

Signed-off-by: Peter Jones <pjones@redhat.com>
Don't error on unset BootOrder when we're trying to add to or rm from it.

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