webos-image.bbclass: Fix function for luna-service2 privileged binaries permission warnings

:Release Notes:
Fixes for function which generates warning if luna-service privileged
file is accessible for everybody.

:Detailed Notes:
Some minor fixes for previously merged function.

:Testing Performed:
Build succeeded

:QA Notes:

:Issues Addressed:
[GF-10973] Ensure the LS2 services are executable only by root	24
[GF-37875] CCC: Meta-webos fix for wrong file permissions warning generation.

Open-webOS-DCO-1.0-Signed-off-by: Alexandr Smoktal <alexandr.smoktal@lge.com>

Change-Id: I8b17e44b253f72aa6ddcfd427d509b9aa0bd2518
Reviewed-on: https://g2g.palm.com/3404
Reviewed-by: Build Verification
Reviewed-by: Alexandr Smoktal <alexandr.smoktal@lge.com>
Tested-by: Alexandr Smoktal <alexandr.smoktal@lge.com>
Reviewed-by: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: Keith Derrick <keith.derrick@lge.com>