Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Bugfix: openrc api dump should be safe_dump

    1. fix safe_dump
    2. fix pep8 problem, use flask_restapi custom error handling [1]

    [1] https://flask-restful.readthedocs.io/en/latest/extending.html#custom-error-handlers

    JIRA: YARDSTICK-1165

    RestApi openrc dump clouds.yaml error

    it now use yarml.dump, should be yaml.safe_dump.

    dump would gererate !!python/unicode and cause error when upload openrc file in gui

    Change-Id: Id3e85f7ba7d4967277ef79109b07d7552179e5db
    Signed-off-by: rexlee8776 <limingjiang@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index b7f867b..f1a71b2 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit b7f867ba873806a10972108fa19d26b2ae19fa58
+Subproject commit f1a71b2889da3b49358b10b9a12ea5a512dd2743