Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - fix multi-monitor unitest hang

    need to mock SSH.from_node().execute.return_value
    because we switch most SSH calls to use from_node()
    factory function

    Change-Id: Ibea525c2fcc243d41de8ccbcd40bc98532d69006
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index a5e13df..5271e61 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit a5e13df9381c531716b1e41e7a9dedb130fc6e35
+Subproject commit 5271e612d427b29c2da84f8417f4192427ae3977