Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Terminate openstack service process using kill command in HA test cases

    JIRA: YARDSTICK-659

    In some openstack environment, the service process cannot be killed by killall
    command but can be terminate by kill command.
    This patch is about to switch to use kill command in the
    fault_process_kill.bash to kill processes.

    Change-Id: Iec455ee56d3f31fb5c16de5994870d1acd33f41a
    Signed-off-by: JingLu5 <lvjing5@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 67b56f7..dd42ba3 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 67b56f734f1d2bb77601c2e75e29fd351f70498e
+Subproject commit dd42ba3cafb908246da5b90c8bbbc2c7d0beb801