Update git submodules

Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Change sdnvpn testcases file path

    JIRA: DOVETAIL-458

    1. Functest has changed the repo of sdnvpn.
    2. Currently Dovetail will copy the testcase yaml file to
       /home/opnfv/repos/sdnvpn/sdnvpn/test/functest/config.yaml in Functest container.
    3. The path needed to be replaced by
       /usr/local/lib/python2.7/dist-packages/sdnvpn/test/functest/config.yaml

    Change-Id: I1badba4120e96e2c9ed5a07db3189967cf24c564
    Signed-off-by: xudan <xudan16@huawei.com>