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>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 1261ce7..60291ea 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 1261ce7747b463a0f70d228567be4829d43d148f
+Subproject commit 60291ea30d941559e3d380d435a495502b3c80b9