molecule job refactorings

Summary of discussions made with rfolco around ci-config molecule jobs.

Note about action items: they are supposed to implemented gradually, job by job.

First POC job

The first job that already uses this newer setup is mol-promoter:

move all molecule scenarios to repository ./molecule
convert all jobs not based on "mol" job to inherit from them
Periodic mol jobs are to be defined in the same location as their check and gate ones, not in other repos (rdo-jobs). Cross-repo dependencies hinders refactoring
Assure voting is never specified in job declaration,
and is only accepted in definition (gate/check/…)

Given a job name mol-foo, developer would be sure it can run the same scenario locally using molecule test -s foo
Removing default scenario as it proved to cause confusions