db: prettified_cmd should contain the command submitted by the user

[diegodelemos]

In #61, since the old way of retrieving the command submitted by the user was breaking some use cases of the cwltest we just used the wrapped_cmd (see here). We should find a new way of retrieving the command so prettified_cmd can be used to be shown to the user in the CLI or the UI.

In kind of pseudocode:

wrapped_cmd = cwl_engine_prefixes + expand_variables(user_provided_cmd) + cwl_engine_postfixes
# whereas
prettified_cmd = expand_variables(user_provided_cmd)