checking_error still used while it shouldn't

[maikia]

The dispatcher sometimes sets the checking_error:

ie:

ramp-board/ramp-engine/ramp_engine/dispatcher.py

Line 170 in a2f585f

set_submission_state(session, submission_id, 'checking_error')

this should no longer be used:

ramp-board/ramp-database/ramp_database/model/submission.py

Line 40 in fa193ac

'checking_error', # not used, checking is part of the workflow now

It is also quite confusing for the challenge participant.

Participants might find something like this under my submissions tab, under the errors:

While the link to the training_error leads to the information about the python error, the checking_error is an error coming from sending submission (ie, problem with the connection, problem with setting up an instance etc). However the participant does not receive any information about the nature of the problem:

This is confusing.

[rth]

Maybe we can create an enum with all valid states, and use it in all workers? As right now we use states as string, and have this issue that state we compare against can have typos (#469) or have deprecated states, which is hard to detect.

With an enum we would be able to detect such issues with mypy I think.