Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Fix for datasource field value"
  - Fix for datasource field value

    This is fix for grafana dashboard templates
    where variable "${DS_YARDSTICK}" is replaced
    by "yardstick".

    JIRA: YARDSTICK-1089

    Change-Id: I0647d5bfd772a2d9ffa18bac59cdbbb39c8ec0ab
    Signed-off-by: Mika Rautakumpu <mika.rautakumpu@nokia.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 38e1403..973853d 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 38e14036886658e87d3c54d7bfc6a364ac5b75f3
+Subproject commit 973853de78ebdf312779ba87c72130334ef0c6f3