Propagate JENKINS_JAVA_HOME to Jenkins process as JAVA_HOME

This was working correctly for JBoss and Tomcat controllers, Winston controller
was affected. Effectively fixed once https://github.com/jenkinsci/lib-process-utils/pull/1
is integrated.

Using wistone controller JAVA_HOME was propagated to Jenkins and further to processes
launched form it. And since Java 8 is used on jenkins.ci.cloudbees.com to run harness,
plugins.FindbugsPluginTest.build_simple_freestyle_mavengoals_project because of
https://jira.codehaus.org/browse/MFINDBUGS-194.
Simplify JENKINS_HOME setting for Local controller
Fix NodeLabelParameterPluginTest#run_on_a_particular_offline_slave