Disable service discovery when instantiating obspy client

When instantiating an obspy client, several requests are sent to resif to discover available services. We don't need that and it may represent thousands of requests each day. Let's disable this.

Moreover if service discovery fails (50X return codes), get_waveforms and get_stations may later raise a ValueError (saying that dataselect and/or station services are not served by the datacenter). Disabling service discovery avoid those side effects