Remove trace from api exceptions

[benchdoos]

If there is an exception during request, response dto contains trace log:

{
  "timestamp": "2020-04-13T09:11:05.547+0000",
  "status": 500,
  "error": "Internal Server Error",
  "message": "No message available",
  "trace": "java.lang.NullPointerException\n\tat com.github.benchdoos.meetroom.controller.api.v1.ApiV/.....",
  "path": "/meetroom/api/v1/user/change-username"
}

Trace must be moved.