Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Implement Virtual Switch resilience test case"
  - Implement Virtual Switch resilience test case

    This testcase tests the resilience of the Virtual
    Switch in an OpenStack environment. It can only run in a
    non Ubuntu distro because it is limited by this bug [0]

    [0]: JIRA: YARDSTICK-1140

    Change-Id: Ia1480fba9f3549d1144c80699056b501d3b07a0f
    Signed-off-by: Dimitrios Markou <mardim@intracom-telecom.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 5c7b893..fe8aac3 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 5c7b8938e79843b1c9a7883aa5c95a81634ecc9d
+Subproject commit fe8aac36f1f66c29bd68c4bc0e22c9de077a1fad