Update git submodules

Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Merge "Specify valid external network as an env"
  - Specify valid external network as an env

    In some deployments, the retrieved external network by the
    def get_external_net checked by "router:external" is not available.
    So it is necessary to specify the available external network
    as an env by user for some deployments.

    JIRA: FUNCTEST-865

    Change-Id: I561bc7d57e06214516a4cdbebd67632cd9746fba
    Signed-off-by: Linda Wang <wangwulin@huawei.com>