Fix incorrect use of variable arguments in run_parts() and simplify code

The run_parts() implementation used variable arguments in a bad way,
resulting in it not working properly.  Replaced va_*() code with a
simple cmd argument that's passed to each script called.

Also, the opendir()/readdir() code has been replaced with scandir()
using regular alphasort(). This simplifies the code somewhat as well.

Otherwise, minor cleanups.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

finit.c

@@ -185,7 +185,7 @@ int main(int UNUSED(args), char *argv[])
 	 */
 	if (rcsd && fisdir(rcsd)) {
 		_d("Running startup scripts in %s ...", rcsd);
-		run_parts(rcsd);
+		run_parts(rcsd, NULL);
 	}
 
 	/*