Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "HA testcase improvement"
  - HA testcase improvement

    This patch improve HA test case in the following aspects:
    1. the "GeneralHA" type now will check if the target service process in the controller node.
    2. support ignore server certificate
    3. add debug log for recovering service failed
    4. improve method to kill keystone process

    Change-Id: I9ae7ab54391fe41d5d7f3e4951a7ac2e3ba75968
    Signed-off-by: JingLu5 <lvjing5@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index a6eed79..6b3ee75 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit a6eed7930c01d59b8511edec76cdae8c9ef5c94a
+Subproject commit 6b3ee75dc0b5fc0e66c914d0b72b4396411526fd