Update git submodules

Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Merge "Support to specify the valid external network name"
  - Support to specify the valid external network name

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

    Change-Id: I333e91dd106ed307541a9a197280199fde86bd30
    Signed-off-by: Linda Wang <wangwulin@huawei.com>