Configure users at build time
use extrausers
package and EXTRA_USERS_PARAM
for configuration on image level.
https://wiki.yoctoproject.org/wiki/FAQ:How_do_I_set_or_change_the_root_password
https://www.yoctoproject.org/pipermail/yocto/2015-April/024610.html
https://git.yoctoproject.org/cgit.cgi/poky/plain/meta/classes/extrausers.bbclass