Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Sample VFW VNF

    Change-Id: I32ca166cd6d818b57bbcfaf7c7e5a65b7147ba8d
    Signed-off-by: Deepak S <deepak.s@linux.intel.com>
    Signed-off-by: Edward MacGillivray <edward.s.macgillivray@intel.com>
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 4e27e2b..90b70c7 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 4e27e2bc0770311feac849c4e3aac9c5ffac4f3d
+Subproject commit 90b70c723c4c3b731ca3e88f79b7c7e7f1a7c20d