director-v2 unexpected failure when output cannot be retrieved

[pcrespov]

• on output is deleted using the explorer in "Service Data" but it remains in the Outputs. See here results.csv in the third output
  

Since the service expects an output, then the directorv2 fails because the output does not exist and stops from starting!?

SEE https://monitoring.tip.itis.swiss/graylog/messages/graylog_439/3b163310-2d57-11ef-8a34-0242ac12000b

NOTE that the error reports an OEC, i.e. it is identified as an unhandled exception. Practically, the services does not start ever and the user is not even informed of the OEC.

Probably this is due to the bad handling of web-server errors. This is being redesigned in #5487

CC: @Konohana0608