Update git submodules

Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Disable restricts of sdnvpn test cases

    1. The original testcases.yaml file of Functest restricts sdnvpn test cases
       to run on Fuel, Apex or Netvirt on bgpvpn scenario.
    https://github.com/opnfv/functest/blob/master/functest/ci/testcases.yaml#L278
    2. Dovetail has a testcases.yaml file to allow sdnvpn test cases run on
       any commercial SUTs.
    https://github.com/opnfv/dovetail/blob/master/etc/userconfig/testcases.yaml#L113

    Change-Id: I0d5ed5b22e55dc3dc0fe584dc57b28239334b7de
    Signed-off-by: xudan <xudan16@huawei.com>