Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Read user & password from yardstick.conf in Grafana configuration"
  - Read user & password from yardstick.conf in Grafana configuration

    JIRA: YARDSTICK-812

    Currently grafana data source configuration is hardcoding .
    It is a risk.
    so I read it from yardstick.conf.

    Change-Id: I8a9c8afbce6c4534fc43a0bfb5c56d67a8b59db0
    Signed-off-by: chenjiankun <chenjiankun1@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 8eedebe..cb63cb9 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 8eedebec3bca3dc6e588c06073b3ad367dfd36b1
+Subproject commit cb63cb9ed232dc40ce118e1b8c001841552ff808