Generate native xml format of Jenkins Git plugin version 2.x

  * the current generated xml is based on Jenkins Git plugin version 1.x
    and relies on auto migration feature of version 2.x, which does not
    work with nunber of git options e.g. fastpoll, shallow-clone
  * the introduced fix generate xml directly to 2.x format
  * as consequence the Jenkins Git plugin version 1.x is no longer supported