Merge requests contain their own description which is comparable to a
`git send-mail` cover letter.

If the merge requests contains only a single commit the merge request
description equal commit description per default. If the merge request
contains multiple commits the description is user defined and ideally
contains a summary of the proposed commits.

For CI purposes the merge request description can contain commands
change the CI default behaviour. This is useful to explicitly run
special cases.

The merge request description could contain a control command like the
following:

```
CI-config: USE_SPECIAL_CASE_Z=1
```

The CI script can evaluate those options via the following command:

```
echo "$CI_MERGE_REQUEST_DESCRIPTION" | grep -e "^CI-config:" \
	cut -d ':' -f 2 | tr ' ' '\n' > extra_env
```

This method allow to run corner cases withouth modifying nor bloating
the git log.
Signed-off-by: Paul Spooren <mail@aparcar.org>