show a message instead of failing when using the conversion-service api client
Created by: hixi
For the status and other requests going to the conversion-service, generate a default message when it is not reachable or returns in an erroneous state. After discussion, we agreed that this should be done on the osmaxx.excerptexport.services.conversion_api_client.ConversionApiClient
or even further up (caller side), out of the following reasons:
- simpler to create defaults in python than json objects, whereof we often only need one entry
- easier to define a timeout for unresponsiveness in specific cases
- visibility of exception handling is better
- no guessing for what kind of case it covers