webos-image.bbclass: Don't check perms on LS2 services in /usr/sbin

:Release Notes:
Exclude LS2 service executables in /usr/sbin from the file permissions
check because this directory is not accessible by jailed applications.

:Detailed Notes:

:Testing Performed:
Built successfully. Ran MiniBAT.

:QA Notes:

:Issues Addressed:

[GF-46366] Fix LS2 service and roles file QA issue output from do_rootfs
[GF-56539] CCC: webos-image.bbclass (exclude LS2 services in /usr/sbin
           from permissions check)

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

Change-Id: I022342f9a7401a317bc72a5c183973ffae0aacd0
Reviewed-on: https://g2g.palm.com/4260
Reviewed-by: DCO Verification
Reviewed-by: Jongho Kim <jongho1208.kim@lge.com>
Tested-by: Jongho Kim <jongho1208.kim@lge.com>