Update git submodules

* Update docs/submodules/yardstick from branch 'stable/danube'
  - Bugfix: remove test.dbf file in recovery script

    JIRA: YARDSTICK-696

    Change-Id: I09b73079ff828c43040723794115bb07f74242e8
    Signed-off-by: zshi <zshi@redhat.com>
    (cherry picked from commit d578927cd63784616f11c4d669815192fd5fa336)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 1dae2ed..d609aa7 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 1dae2ed45bb425de276441c99da64b21ee4f97de
+Subproject commit d609aa7438e543354debfe86ab9d34a0e6402eda