Update git submodules

* Update docs/submodules/stor4nfv from branch 'master'
  - Add openstack test case

    Change-Id: Ib14ffc283dd4226810e2388807971ae97d25e122
    Signed-off-by: Qiaowei Ren <qiaowei.ren@intel.com>

diff --git a/docs/submodules/stor4nfv b/docs/submodules/stor4nfv
index 4ced57e..df4ff81 160000 (submodule)
--- a/docs/submodules/stor4nfv
+++ b/docs/submodules/stor4nfv
@@ -1 +1 @@
-Subproject commit 4ced57eae63a52ea517d4087662726d942da8441
+Subproject commit df4ff81d7e0d296b74c17957817cba4137756db8