Enable asserts for testing builds

:Release Notes:
Enable assert for in luna-service2 if WEBOS_DISTRO_PRERELEASE == devel

:Detailed Notes:
Currently assert are disabled for all release builds.
Enabling for testing images will help to interpret unexpected crashes.

:Testing Performed:
On device and emulator.

:QA Notes:

:Issues Addressed:
[GF-39090] LS2: Enable asserts for testing builds

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

Change-Id: I1fb95abb76191802c467e2ecef087d924b9f17fb
Reviewed-on: https://g2g.palm.com/3658
Reviewed-by: Build Verification
Reviewed-by: Alexandr Smoktal <alexandr.smoktal@lge.com>
Tested-by: Alexandr Smoktal <alexandr.smoktal@lge.com>
Reviewed-by: Keith Derrick <keith.derrick@lge.com>
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>