init-live.sh: fix overlay fs

init-live.sh: fix overlay fs

* The name changes from overlayfs to overlayo
* The workdir is a must when mount
* The updir must be a subdir of rootfs.rw

This patch plus with another one which has been sent to linux-yocto can
fix the error when boot iso:
EXT4-fs (loop0): re-mounted. Opts: data=ordered
Populating dev cache
/etc/init.d/rc: /etc/rcS.d/S37populate-volatile.sh: line 1: can't create
/etc/volatile.cache.build: Read-only file system
/etc/rcS.d/S36udev-cache: line 73: can't create /etc/udev-cache.tar.gz:
Read-only file system
udev-cache: update failed!
rm: can't remove '/etc/udev/cache.data': Read-only file system
/etc/init.d/rc: /etc/rcS.d/S37populate-volatile.sh: line 1: can't create
/etc/volatile.cache.build: Read-only file system
/etc/init.d/rc: /etc/rcS.d/S37populate-volatile.sh: line 1: can't create
/etc/volatile.cache.build: Read-only file system
/etc/init.d/rc: /etc/rcS.d/S37populate-volatile.sh: line 1: can't create
/etc/volatile.cache.build: Read-only file system
/etc/init.d/rc: /etc/rcS.d/S37populate-volatile.sh: line 1: can't create
/etc/volatile.cache.build: Read-only file system
/etc/init.d/rc: /etc/rcS.d/S37populate-volatile.sh: line 1: can't create
/etc/volatile.cache.build: Read-only file system
/etc/init.d/rc: /etc/rcS.d/S37populate-volatile.sh: line 1: can't create
/etc/volatile.cache.build: Read-only file system
/etc/init.d/rc: /etc/rcS.d/S37populate-volatile.sh: line 1: can't create
/etc/volatile.cache.build: Read-only file system
/etc/init.d/rc: /etc/rcS.d/S37populate-volatile.sh: line 1: can't create
/etc/volatile.cache.build: Read-only file system
rm: can't remove '/tmp': Read-only file system
ln: /tmp/tmp: Read-only file system
/etc/init.d/rc: /etc/rcS.d/S37populate-volatile.sh: line 1: can't create
/etc/volatile.cache.build: Read-only file system
/etc/init.d/rc: /etc/rcS.d/S37populate-volatile.sh: line 1: can't create
/etc/volatile.cache.build: Read-only file system
/etc/init.d/rc: /etc/rcS.d/S37populate-volatile.sh: line 1: can't create
/etc/volatile.cache.build: Read-only file system
ln: /etc/resolv.conf: Read-only file system
/etc/init.d/rc: /etc/rcS.d/S37populate-volatile.sh: line 1: can't create
/etc/volatile.cache.build: Read-only file system
/etc/init.d/rc: /etc/rcS.d/S37populate-volatile.sh: line 1: can't create
/etc/volatile.cache.build: Read-only file system

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>