Test insertion / update of multi-lingual metadata records

[eblondel]

In relation with eblondel/geometa#104

[eblondel]

For unknown reasons, insert of multilingual metadata return an Internal Server Error, although, on R side, the GN request XML payload is correctly encoded. Further investigation to be done to see if it is an issue in Geonetwork

[eblondel]

This works well on GN >= 3.0 . Attempts on a Geonetwork 2 are unsuccessful which let assume issues with the Geonetwork 2 software.