Simplify the choice of the runtime system before integrating the new ones

Simplifies the way we choose the runtime before integrating PR !106 (closed) and !108 (merged)

added 3 commits

• cd725fad...c0c86d69 - 2 commits from branch solverstack:master
• faffa860 - Simplify the choice of the runtime system before integrating the new ones

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@fpruvost @viroulea @agullo Please have a quick look. I would like to merge it before !106 (closed) and !108 (merged). Thanks

Perfect for me!

merged

mentioned in commit a4a509da