Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Replace glance create image with shade client."
  - Replace glance create image with shade client.

    Function create_image now uses shade client.

    JIRA: YARDSTICK-892

    Change-Id: Ia41d9ce702a1f24031080f8a365c1b2bd9ac9faa
    Signed-off-by: Shobhi Jain <shobhi.jain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 1da4bb5..2e6ac12 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 1da4bb59dac46e40d580ce7e16fddc19991f609c
+Subproject commit 2e6ac1229309227398cb651e68ec062dbb95c955