Added test method and test documatations

This method has mentioned as the steps updated in tests-obs/README.md.

The test method provides a Makefile that may run make to build tests/obs-api, tests/obs-server, tests/worker images based on previous docker images with apt upgrade to ensure it has latest packages installed from upstream.

User should fetch their latest OBS binaries packages and places under /tmp/binaries. The docker compose file will bring up tests containers with volume set /tmp/binaries/ where the fetched binary localted.

The update-obs-binaries.sh may help to run dpkg -i in each test containers to update to the latest OBS packages that fetched under /tmp/binaries/.

If anything broken and want to get a clean installation. May just run make clean to clean up the containers and restart again with new package that you built in your OBS.

Signed-off-by: Andrew Lee (李健秋) andrew.lee@collabora.co.uk