Remove plateforme based integration testing

Using `JenkinsRule` enable to run Jenkins-Client Integration Tests anywhere and setup the "Jenkins environment" we want to query using Jenkins-Client classes.

The maven property `jenkins-version` enable to run integration test against any Jenkins version greater than "1.537", creation of the `JenkinsRule` class. So we can use

    mvn clean verify -Djenkins-version=1.563

to validate the library againt Jenkins 1.563 version.

closes RisingOak/jenkins-client#25