Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Bugfix: cleanup command not found"
  - Bugfix: cleanup command not found

    JIRA: YARDSTICK-808

    This bug is from CI, see log:
    https://build.opnfv.org/ci/view/yardstick/job/yardstick-joid-baremetal-daily-master/1560/consoleFull

    The reason is we don not have cleanup function in the script.
    It is in another script clean_image.sh.
    so I remove it, and call clean_image.sh when in openstack scenario.

    Change-Id: I844cd9e8f0b6e1e8ff7a6094be37789d35a2c345
    Signed-off-by: chenjiankun <chenjiankun1@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 3344f06..aff74a1 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 3344f0671b911b7a31c2cbf2ae3051b05af21d4c
+Subproject commit aff74a1ac608b430dc10d62e3ea543c3061586ce