private void disconnect() {
    if (system != null) {
      system.disconnect();
      system = null;
    }
  }
Creates a fresh loner DistributedSystem for each test. Note that the DistributedSystem is the
StatisticsManager/Factory/etc.
geode-core/src/integrationTest/java/org/apache/geode/internal/statistics/GemFireStatSamplerIntegrationTest.java