Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Test Case: OPNFV_YARDSTICK_TC023: VM availability during live migration"
  - Test Case: OPNFV_YARDSTICK_TC023: VM availability during live migration

    JIRA: YARDSTICK-174

    This live migration test case is based on share storage, default share
    storage is enabled.
    This test case will do some config work. And do live migration and
    calculate the migration time and downtime.

    Change-Id: I6601601edebdd0ac6434ba632b1eba9e9bd4fda0
    Signed-off-by: chenjiankun <chenjiankun1@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index cf68baf..355601a 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit cf68baf48f43ebb70b1fb137fd4f1a5bbbc1e0df
+Subproject commit 355601ab1b2335550905574148b097292f214325