utils: use common code for apply_rules and apply_cipso

utils: use common code for apply_rules and apply_cipso

Code for apply_rules() has been rewritten to use opendir() and readdir(),
but apply_cipso() remained implemented with nftw().
This patch implements both applying functions with opendir() and readdir()
using a common internal function apply_path(). The common function can
handle both directory and single file,  so apply_rules_file() and
apply_cipso_file() are dropped.
The resulting code is 69 lines shorter and keeps directory traversal logic
in single place. It's side effect is applying CIPSO rules in one shot, just
like regular Smack rules.

Signed-off-by: Rafal Krypa <r.krypa@samsung.com>