installer: fixed multiple random issues.
installer: fixed multiple random issues.

- there's no need to check if $SYSTEMD_INIT==1, just test if it's set.
- set TIMEZONE correctly to /etc/rc.conf.
- Set fstab(5) fs_passno correctly for the rootfs and additional filesystems.
- Disable fsck if rootfs is f2fs, it does not work correctly.

yopito/void-mklive,enguerrand/void-mklive,thypon/void-mklive