initscripts: update populate-volatile.sh

initscripts: update populate-volatile.sh

If a partition such as /tmp mounted on a volatile directory which create
by script populate-volatile.sh from initscripts, it will show errors.

In /var/log/boot, error message:

Thu Jun 19 05:39:09 2014: bootlogd.
Thu Jun 19 05:39:10 2014: rm: cannot remove '/tmp': Device or resource busy

Check volatile directories and if it is be mounted then don't force make
it as a link.

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>