Convert xqueue gunicorn configuration to file

Per the mailing list discussion (https://groups.google.com/d/msg/openedx-ops/kHTfBuVr6ko/1XKWaFyh50gJ), here is the conversion of xqueue to using a conf file.  It ends up looking a bit cleaner.  Should I just submit a PR for each service I convert, or would you prefer I just do them all in one? @feanil