As otto and I have been trying to package auth_socket.so install this plugin during install.
As Jean and I noticed https://lists.launchpad.net/maria-developers/msg08317.html you can't install a plugin during bootstrap as it automaticly enables --skip-grant-tables (effectively).
While you can insert into the plugin table directly this skips the init routes in the plugin, fine for auth_socket since it doesn't have any, however its a bad practice we probably don't want to encourage.
patch: https://github.com/MariaDB/server/pull/29