Make ci work in fork.

[JeroenKnoops]

Currently the CI scripts fail in forks.

This can cause issues which can only be found when:

1. Running it locally
2. Merging it into the upstream

[JeroenKnoops]

Maybe we can do something when the mandatory parameters (like DOCKER_ORGANIZATION) are not set. If not set, set a good default and only run the build and not the push or something like that...

[JeroenKnoops]

In docker_build_and_push.sh we check if we need to publish the docker image to dockerhub.
We might build an extra check there.

Check the first part of repository name ( github.repository : f.e. philips-software/docker-ci-scripts ) with the GITHUB_ORGANIZATION variable. If you have forked it, this will be different, therefore you don't want to push it to dockerhub.