Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Test case description and configuration file for yardstick_tc090:Control Node Openstack Service High Availability - Database Instances"
  - Test case description and configuration file for yardstick_tc090:Control
    Node Openstack Service High Availability - Database Instances

    JIRA: YARDSTICK-960

    Change-Id: Ibe47a9b4d1f095971857fcbaee57a3c7f64f9911
    Signed-off-by: tjuyinkanglin <14_ykl@tongji.edu.cn>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 4b60891..0c64be3 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 4b60891a8b0a23d785053b7d99a973b4e83e0a1e
+Subproject commit 0c64be36cd7820c46dd68bffda47fab6fc56ae94