Support for Jenkins2 Pipeline

In Jenkins2 Pipeline, Datadog Event Monitor is unstable work.
Maybe cause, in Jenkins2 Pipeline, [run.getDuration()](https://github.com/DataDog/jenkins-datadog-plugin/blob/master/src/main/java/org/datadog/jenkins/plugins/datadog/DatadogBuildListener.java#L211) is always return 0.
