populate-volatile.sh: improve the handling of link config items

populate-volatile.sh: improve the handling of link config items

Previously, if there's a link config item in the config file like

	    l root root 1777 /tmp /var/tmp

and /tmp has existed, the symlink will not be created correctly.

Another example is the /run directory. If /run directory has been
created by some recipe or script before populate-volatile.sh runs,
the symlink of /run to /var/run will not be created correctly.

This patch ensures that the system creates symlinks exactly as the
config file tells it.

[YOCTO #3404]
[YOCTO #3406]

(From OE-Core rev: a54287d8e3d75a727c8ed5654a822bda256b0849)

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>