ServletEngineExecutor is not using the proper java version to inject the add-opens

We are currently injecting the --add-opens modules for running docker tests with Jetty when the version of Java that is running test is 17. The check should actually be done on the version of Java of the container.

Moreover, right now there's a problem with those --add-opens when running the tests with jetty:10-jdk11 or jetty:10-jdk17, the container never starts with an error:

Error: --add-opens requires modules to be specified

The command line indeed contains:

/opt/java/openjdk/bin/java -Djava.io.tmpdir=/tmp/jetty -Djetty.home=/usr/local/jetty -Djetty.base=/var/lib/jetty --add-opens -Djava.io.tmpdir=/tmp/jetty