"allow root login" should not be bundled in ssh_allow_empty_password,
because some distro may want only one of "allow root login" and "allow
empty password", so split it out into ssh_allow_root_login and add new
imagefeature allow-root-login so they can be controlled separately,
debug-tweaks will still include both of them.
Signed-off-by: Jackie Huang <jackie.huang@windriver.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
