Update git submodules

Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Committer promotion Dan Xu and removal of Leo Wang

    Contributions Dan Xu:
    Dan Xu has been almost exclusively doing the development for the
    Dovetail tool, CI integration, and the practical validation of test case
    candidates.
    https://gerrit.opnfv.org/gerrit/#/q/owner:%22Dan+Xu+%253Cxudan16%2540huawei.com%253E%22

    Leo Wang has announced that he is stepping down as committer from the
    project. Thank you for your contributions to the project.
    https://lists.opnfv.org/pipermail/opnfv-tsc/2018-February/004130.html

    Change-Id: I14032657b057bdd3da1f9c3514b3c27e34dbafc0
    Signed-off-by: Georg Kunz <georg.kunz@ericsson.com>