Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "substitute with testapi img"
  - substitute with testapi img

    delete useless openstack and refstack images
    add testapi-logo.png. Currently it is a free one with signature
    finally we will substitute it with an official one.

    Change-Id: I6c1ccaa21fab311c5858351e58bd7c8d9392a75a
    Signed-off-by: SerenaFeng <feng.xiaowei@zte.com.cn>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 66b066c..9a2ffa4 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 66b066c839641cfd7a4604af6f111d07dc50f595
+Subproject commit 9a2ffa4606cbc724ad11ffa8ac79c92c72069b2f