Update git submodules

* Update docs/submodules/openretriever from branch 'master'
  - Add ping vnf

    Change-Id: Ia58832589385f2be2309f60f0567fae3635c7833
    Signed-off-by: Guo Ruijing <ruijing.guo@intel.com>

diff --git a/docs/submodules/openretriever b/docs/submodules/openretriever
index edea600..dc766e6 160000 (submodule)
--- a/docs/submodules/openretriever
+++ b/docs/submodules/openretriever
@@ -1 +1 @@
-Subproject commit edea600a65fa5879c564c2f8de3bbbf1d91f7823
+Subproject commit dc766e69c0c08c55b6df2384bbcfd1e712f03160