Fix build against gtest in webOS environment

:Release Notes:
The source code of gtest should be referred via cmake module.

:Detailed Notes:

:Testing Performed:
Build and unit tests.

:QA Notes:

:Issues Addressed:
[BHV-1535] Investigate existing wrappers

Open-webOS-DCO-1.0-Signed-off-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>

Change-Id: I76ba048af1e200cde13c23d5dd8bc13c47ad09fe
Reviewed-on: https://g2g.palm.com/5142
Reviewed-by: DCO Verification
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>
Tested-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>
Reviewed-by: Nikolay Orliuk <nikolay.orliuk@lge.com>