Unintentional hardcoding of THREDDS server

[corviday]

In routes.py, the location of the THREDDS server is dervied by parsing the URL string; however, as the URL string does not contain the location of the THREDDS server, the default value (marble-dev01) is always the result.

The location of the THREDDS server should be derived from environment variables using os.getenv(), as it is elsewhere in the codebase, allowing it to be set at runtime.