Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "move flatten dict key to common utils"
  - move flatten dict key to common utils

    So it can easily be used by other testcase to unify result

    JIRA: YARDSTICK-702

    Change-Id: Id4fde38a9a0c2a87a6c870bdb7b0c8f3a3b371ac
    Signed-off-by: rexlee8776 <limingjiang@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 917dea4..2bea82e 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 917dea49415183eaff6d2f2fbf32ddeff64d9dfe
+Subproject commit 2bea82e39d62246552a9d6d49c74bbc32747f018