Add support for building the unit tests

- Add targets to compile unit tests: core, performance, stress, database client tests.
- The building of the unit tests is enabled via by setting WEBOS_CONFIG_BUILD_TEST.
- Add luna system bus permissions files for the unit tests.

Open-webOS-DCO-1.0-Signed-off-by: Maksym Sditanov <msditanov@luxoft.com>

Change-Id: Iefe624f29f17faee056142d99c823d94c60a0deb