Update git submodules

* Update docs/submodules/openretriever from branch 'master'
  - Merge "Add ping vnf using vhost-user & virtio-user"
  - Add ping vnf using vhost-user & virtio-user

    Change-Id: If1138e90dd5ebf3c4748dc9cc998c93bb037c4c7
    Signed-off-by: Guo Ruijing <ruijing.guo@intel.com>

diff --git a/docs/submodules/openretriever b/docs/submodules/openretriever
index d14bcec..5812982 160000 (submodule)
--- a/docs/submodules/openretriever
+++ b/docs/submodules/openretriever
@@ -1 +1 @@
-Subproject commit d14bcec5cbfaa1972fafdd3e1ad849f1014a4360
+Subproject commit 5812982c9b2c84aaa6bba36ac6a06ed025dd7e10