yadage: write logs to a canonical file

[diegodelemos]

It would be of great help to have the workflow logs written to a canonical file as well, so everything would look like:

# as workflow's logs
/reana/analyses/:uuid/workspace/logs/workflowuuid.log
# as step's logs  # as step logs
/reana/analyses/:uuid/workspace/logs/stepuuid.log

[lukasheinrich]

this will be the job of reana-job-controller but the engines can play the role of managing the locations to a canonical one that makes sense within a workflow

i.e.

engine --- submit job spec ---> job-controller
engine <--- retrieve logs ------ job-controller
the engine then writes the logs where it wants to

[diegodelemos]

yes, this is what you proposed last time, but it was not clear how to implement it with yadage back then, is it clear now?