[docker] jetty container now uses java-headless

[pmauduit]

Previously, the classic JRE was installed in the upstream docker image for jetty. Now it is the headless version of the JRE which is installed, making some GN features to fail (WMS harvesting with automatic getmap picture generation activated).

Steps to reproduce

1. create a WMS harvester node
2. http://geo.somme.fr/arcgis/services/SIG_CG_SOMME/MapServer/WMSServer as WMS1.3
3. Getting the error about the class org.GNOME.Accessibility.AtkWrapper not resolveable.

[fvanderbiest]

probably still relevant I guess...

[pmauduit]

Not sure, I just retried onto geop-dev, and the pcitures are actually generated on the harvested MDs.