Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Test case description and configuration file for yardstick_tc088"
  - Test case description and configuration file for yardstick_tc088

    JIRA: YARDSTICK-958

    Change-Id: I4b9633deca5b88c836aaeea02454495381fe5843
    Signed-off-by: tjuyinkanglin <14_ykl@tongji.edu.cn>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 54bfc1b..8ef8459 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 54bfc1b0a9372cb2efc9dc75d504adc805f503c1
+Subproject commit 8ef84599e72d0ed2f73322ef90300759ce1dbf5c