tests: introduce gtest_mojocore testsuite

- migrate test for MojAtomicInt
- add thread-safety test for MojAtomicInt

Open-webOS-DCO-1.0-Signed-off-by: Nikolay Orliuk <norluk@luxoft.com>
Change-Id: I967f39869e3a47eddf2d967a2d2061adbd9d23c9
Reviewed-on: https://g2g.palm.com/2274
Reviewed-by: Build Verification
Reviewed-by: Nikolay Orliuk <norluk@luxoft.com>
Tested-by: Nikolay Orliuk <norluk@luxoft.com>
Reviewed-by: Maksym Sditanov <msditanov@luxoft.com>
Reviewed-by: Roger Stringer <roger.stringer@lge.com>