Update git submodules

Update git submodules

* Update docs/submodules/sdnvpn from branch 'master'
  - Refactor imports and invocation of main function

    In all testcases there are some inconcistencies of
    import statements. Additionally the main function
    of each testcase should be called through
    sys.exit(main())

    JIRA: SDNVPN-173

    Change-Id: I6fdf0dc6598ca4789b6de6b50d1b8b85a8de923c
    Signed-off-by: panageo2 <panageo@intracom-telecom.com>