Update git submodules

Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Adapting local docs build and remove build warnings

    The OPNFV docs project will remove its submodules and enable local docs
    builds. This patch prepares the Dovetail repo according to the official
    transition guide:

    https://docs.opnfv.org/en/latest/how-to-use-docs/local-build-transition.html

    This patch also applies syntactical changes which eliminate the sphinx
    doc build warnings.

    Change-Id: Ief8fd2d1c3e39b232d214a9ab392879ee4a492c8
    Signed-off-by: Georg Kunz <georg.kunz@ericsson.com>