Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Open storperf testcase to huawei-pod2"
  - Open storperf testcase to huawei-pod2

    JIRA: YARDSTICK-712

    Change-Id: If91c936a3a59580a987cb6762db5d063edf6c9d7
    Signed-off-by: JingLu5 <lvjing5@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index deccb02..15d807c 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit deccb02a8adabe609c2e903ce9f60e8b39db6c29
+Subproject commit 15d807c22f33fab8e1f9b61e1d0c041a8144ee89