core-image.bbclass: zap root password if debug-tweaks not enabled
If you do not have debug-tweaks in IMAGE_FEATURES, then zap the root
password so that you can't log in as root without a password in an image
potentially intended for a production system.
Also mention debug-tweaks in the comments listing IMAGE_FEATURES in this
file.
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
