Update git submodules

* Update docs/submodules/yardstick from branch 'stable/danube'
  - Merge "HA testcase improvement" into stable/danube
  - 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>
    (cherry picked from commit 5b99f1532ec4d15258ec86e970acd2904954b3bc)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index b93bbc0..6e3cb93 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit b93bbc01bf90d4fe6defb137145e74aee8c3081e
+Subproject commit 6e3cb9346cb11acd6bf0882bd7f715b879246909