Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Add API(v2) to delete container"
  - Add API(v2) to delete container

    JIRA: YARDSTICK-729

    API: /api/v2/yardstick/containers/<container_id>
    METHOD: DELETE

    Change-Id: I4cda76329edd7b988a357f1fcb2b5041bf48be64
    Signed-off-by: chenjiankun <chenjiankun1@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index dec0be6..df77b65 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit dec0be619a3968b0a30de710d83636c372f75574
+Subproject commit df77b6585cb54d2e4691b946ea1bc9cca637c108