when new job is started it has "unofficial" job status == "started"

[VMois]

Discovered in reanahub/reana-workflow-engine-yadage#212 (comment)

r-job-controller when successfully starting a new job and returns started status but such status doesn't exists in "official" reana-db component (JobStatus in models.py).

This may affect more engines and needs discussions.

[mdonadoni]

Note that r-w-e-yadage relies on this:
https://github.com/reanahub/reana-workflow-engine-yadage/blob/8f18751696f0ebbf5c0d08b08d9c3e58ee3e3897/reana_workflow_engine_yadage/externalbackend.py#L161
https://github.com/reanahub/reana-workflow-engine-yadage/blob/8f18751696f0ebbf5c0d08b08d9c3e58ee3e3897/reana_workflow_engine_yadage/externalbackend.py#L174