Allow to use the JAVA_HOME environment for cassandra tests
This allows to enforce a specific version of java to be used. For example, since cassandra seems not to support java 14 yet, this allows to run tests on bullseye:
JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64/ pytest swh
Migrated from D4826 (view on Phabricator)