Update git submodules

Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Merge "Clone tempest repository in the Docker image"
  - Clone tempest repository in the Docker image

    Rally needs to have a copy of the Tempest repository
    in order to install the verifier. Otherwise, rally will
    clone it automatically anyway.

    This also uplifts the tempest version to 15.0.0 which targets
    Ocata deployments according to [1]

    [1]: https://releases.openstack.org/ocata/

    Change-Id: I30e922a261a4ab1875d48c4754df09426b5f67e4
    Signed-off-by: jose.lausuch <jose.lausuch@ericsson.com>