Update git submodules

Update git submodules

* Update docs/submodules/sdnvpn from branch 'master'
  - Install run_sdnvpn_tests.py in $PATH

    It eases how Functest runs it (see testcases.yaml [1]).
    The former run_tests.py is renamed to avoid duplicated binaries (see
    [2] and [3]).

    [1] https://git.opnfv.org/functest/tree/functest/ci/testcases.yaml
    [2] https://git.opnfv.org/sfc/tree/sfc/tests/functest/run_tests.py
    [3] https://git.opnfv.org/promise/tree/promise/test/functest/run_tests.py

    Change-Id: I50219cad42bf0e085c2edf2e1abe149c2e057a99
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>