Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Proposing Jack Chan as a committer in Yardstick"
  - Proposing Jack Chan as a committer in Yardstick

    Jack Chan has contributed to the Yardstick project in many ways
    Achievements/Contributions include:
    - Kubernetes context
    - GUI
    - Yardstick API
    - Reporting fixes
    - Attending OPNFV Summit Beijing
    - Regularly attending Yardstick meetings

    Change-Id: Ie46a99619365893f3b877822f82f626cf7a36deb
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 415fcdf..171d923 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 415fcdfc0adbcf79dc1ac17e57cc8240a33f597b
+Subproject commit 171d923436e10134565c211b13b8f8b8be1f8f58