Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Test case spec for SDN Virtual Switch resilience."
  - Test case spec for SDN Virtual Switch resilience.

    This is a test case for verifying the proper functionality of
    SDN Vswitches which are located in the Compute nodes of an OpenStack
    environment.
    This test case is unaware of the configuration (non-HA,HA)

    JIRA: HA-34
    JIRA: YARDSTICK-955

    Change-Id: I701bf1f9527b1a31b9cb52e102734e10c4162766
    Signed-off-by: Dimitrios Markou <mardim@intracom-telecom.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 553ffef..b7f867b 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 553ffefcdaa3d4a0ae61f9ce233b620d51b91d51
+Subproject commit b7f867ba873806a10972108fa19d26b2ae19fa58