ECMWF usecase and wrapping so that davai-run_xp returns 0 or 1

[AlexandreMary]

We have planned with ECMWF to include a Davai experiment in their nightly tests suite, ran automatically every night on their develop branch.
For that matter, we need to setup a reduced usecase (e.g. no need to test all kinds of geometries for PGD...)
and wrap the davai-new_xp/davai-run_xp/davai-xp_status, so that it would return 0 or 1 depending on the results of the experiment.

Note that this could also be beneficial towards a more autmoatised CI in ACCORD, in addition to ECMWF context.