Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Bugfix: change monitor command in tc019

    JIRA: YARDSTICK-655

    The original openstack command used for monitoring high availability openstack
    nova-api service in tc019 is "nova image-list", the "openstack image list" command
    used in tc019 now may not correctly show the nova-api service status.
    This is patch swtich the monitor command to "openstack server list".

    Change-Id: I8810f28b4328ceb4d911a3041a24774ae9cae8f0
    Signed-off-by: JingLu5 <lvjing5@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 87559e9..a5e13df 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 87559e992c1f68559950b258146a530c49db9df0
+Subproject commit a5e13df9381c531716b1e41e7a9dedb130fc6e35