Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - html_template: can't use iteritems, use items

    iteritems is not supported in Python 3
    we have to use items()

    Change-Id: Ib923dfea4220eeab311949c9f6f420fef378e98a
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 7d5cc54..bf15098 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 7d5cc542a9bfa35cba6d2b681e0cf5f90bc77d40
+Subproject commit bf15098782f77d750313a60cb2d4ae61529b369d