LTS Container 2.303.1 uses OpenJDK with wrong file encoding

The openjdk-11 used in the Docker build has the default file encoding set to ANSI instead of UTF-8. This is from jenkins systemInfo: 

As we use non ANSI file names, this breaks Jenkins:

 WARNING h.i.i.InstallUncaughtExceptionHandler#handleException: Caught unhandled exception with ID f755cad7-a303-403d-9dde-3e9296ce302d
java.nio.file.InvalidPathException: Malformed input or input contains unmappable characters ...

Because the JAVA_OPTS parameter 

-Dsun.jnu.encoding=UTF-8

doesn't work, we can't fix this. So we can't use the current Jenkins LTS container.

See https://github.com/AdoptOpenJDK/openjdk-docker/issues/105