Detach java agent runtime

If we just use elastic.apm.active=false, no matter how long we wait threads apm-reporter, apm-request-timeout-timer, configuration-reloader, apm-metrics-reporter will still be running. The only way to stop these threads is using stop method.

Please refer the Other Thread to know why I want all threads to be closed, issue with active flag and what are the actions I am taking to dettach the agent.