check install files passed by cmdline

We should not trust cmdline passed by users, always
check the install files passed from cmdline. This restores
the old behaviour which was changed by:

	commit c6c6a08850
	Author: Harald Hoyer <harald@redhat.com>
	Date:   Tue Feb 7 18:26:30 2012 +0100

	    add "install_items" to dracut.conf

Reported-by: Dave Young <dyoung@redhat.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Harald Hoyer <harald@redhat.com>

dracut.sh

@@ -770,7 +770,7 @@ done
 
 if [[ $kernel_only != yes ]]; then
     for item in $install_items; do
-        dracut_install -o "$item"
+        dracut_install "$item"
     done
     unset item