onBoot hook blocks boot process in some cases

See: https://ask.linuxmuster.net/t/lange-boot-zeit-a-start-job-is-running-for-linuxmuster-haelt-den-systemstart-auf/8716/23

Should be solved by putting a timeout of 5 seconds on pulling a kerberos ticket and mounting the sysvol here:
https://github.com/linuxmuster/linuxmuster-linuxclient7/blob/3d7cb5fbefc06603febbd3fb17773e03a1385fda/usr/share/linuxmuster-linuxclient7/scripts/onBoot#L14