MANIFEST_PROJECT, MASTER_BRANCH_MANIFEST, MASTER_BRANCH_PROJECT

The images from the build job can be directly installed from gitlab.
To achive this some changes in the complete pipeline have been needed.

1. The variables used in the build job, like CI_PARAM_IMAGE, ... and
   related variables like BUILDPATH are only valid in the build job now.
2. The build job writes every variable needed in a follow up job into
   build.env. This also includes the url to the fng-install.sh of the
   final image.
3. The build.env file is used as dotenv artifact, as well as normal
   file artifact.
   The dotenv make the written variables automatically available in
   follow up jobs, that are using the aritfacts, like the deploy job.
   The normal file artifact is available via artifact download.
   (I did't found a way to download the dotenv file instead)
4. Some scripts have been added:
   - Find a job inside the pipeline by name, as the id is not known in
     advance.
   - Download all artifacts or one file of the artifacts from a given
     job
   - Download one file of the latest job by name
5. The scripts are used to download the build.env into the test job
   (where not artifacts are needed anymore)
6. The script is sourced and all variables are available inside the
   script.

Additionally this adds a fake build job to the ci-test pipeline, that
copies an image from srv73 and stores it as artifact in a way that a
test-job can run on it, like in the normal yocto pipeline.

This shares YAML code for the following procedures:
- Build environment
- Source code checkout via repo
- SSH key and known hosts setup
- LAVA test submission
- Docker check if build folder is empty

Some gitlab update(?) seem to have changed the behaviour in
variable passing. In the scripts the variables are available
but in the artifacts path does not resolve them any more.
May be it has something to do with the introduction of the
trigger:forward keyword.

Combine all common yaml parts in manifest-pipeline.yml and add
manifest-pipeline-yocto.yml and manifest-pipeline-ci-test.yml
containing the different variable assignments for each environment.

This change implicitly introduces parent-child build job generation in
the ci-test pipeline, like it is done in the yocto pipeline already.
The ci-test build jobs have been moved to build-jobs-ci-test.jinja2
accordingly.

Furthermore rename GITLAB_CI_CURRENT_REV to GITLAB_CI_REVISION and
remove the run conditions from all generated build jobs, since these are
already present in the upstream trigger job.

The repos including these files have to be updated with the new file
and variable names.

The job generation script implicitly passes the OS environment to the
template, so that the template has access to all GitLab CI variables.
Hence there is no need to explicitly pass any of them as command line
arguments.

This change makes the "generate-build-jobs" job more generic, so that
it can be shared with the ci-test pipeline in the future.

If the MASTER_BRANCH_MANIFEST variable is set in the manifest's
.gitlab-ci.yml file, it may not find its way to the generated job,
if it is not explicitly set during generation.
That is done with this patch.

* Move all build, deploy and test stubs to the manifest-build.yml
* Create a new job to generate and trigger the build jobs dynamically
* Add the base jinja2 file for the build jobs.
* Add initial docs for the manifest pipeline
* Remove unused files