Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "bugfix: tc025 should use ipmi to poweroff"
  - bugfix: tc025 should use ipmi to poweroff

    if it use shutdown, it'll take several minutes to shutdown,
    leads to the ipmi power on command fails

    Change-Id: I74b61325cbcc3a6ec070d2fa103accf84f29b0fa
    Signed-off-by: root <limingjiang@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 4bdb5fd..fc57c4e 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 4bdb5fd41f8726453d80f0856ead3de0f7556bb1
+Subproject commit fc57c4e420571aa5f3bc6c492e4e4c5e066aca21