Update git submodules

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

    JIRA: YARDSTICK-751

    API: /api/v2/yardstick/images/action
    METHOD: POST
    PARAMS:
    {
        'action': 'load_image'
    }

    Change-Id: I9554f35c679ae2a861c7922080aa54a1ffc5bac7
    Signed-off-by: chenjiankun <chenjiankun1@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 2d02476..be2da4d 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 2d0247646d8f5b46c41f8429f439133745c5ed14
+Subproject commit be2da4d7ef13f61cfcd9b591a9b00579b896213d