Add support for yum requirements

This merge request implements the installation of "system dependencies" through yum.

This allows the use of the yum_requirements.txt in the recipe folder to add for example OpenGL libraries before doing a round of package creation.

You can see it work on this pipeline: https://gitlab.idiap.ch/beat/beat.editor/pipelines/55102

The pipelines using the single_package.yaml on the master branch will fail because Qt can't load the OpenGL libraries while with this patch, the test phase starts normally even though it fails later on.

This also shows how using relative include statements in the .gitlab-ci.yml file can help test this kind of implementation without affecting other packages.

Fixes #82 (closed)