Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "Download images and map the folder to container"
  - Download images and map the folder to container

    This patch is to accommadate with the change in patch[1]
    Before running the Functest Docker container, downloading all required
    images first and map the folder to the container

    [1] https://gerrit.opnfv.org/gerrit/#/c/34033

    Change-Id: I617bd988caf1fd354cf9ef675661d40742b693c6
    Signed-off-by: helenyao <yaohelan@huawei.com>