Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Prohibit the importation of a list of libraries"
  - Prohibit the importation of a list of libraries

    Some modules can't be imported and used in Yardstick. For example,
    "ansible" has GPLv3 license and can't be used as a library in this
    project without modifying Yardstick license.

    JIRA: YARDSTICK-896

    Change-Id: I9d6bec0493ac50f1051235cc77e81059dfc3e01c
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 2f7f05f..8b2b680 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 2f7f05ff0a46dd8c975fb0680ce812cf444e8ee5
+Subproject commit 8b2b6806d73e3b4e377cb8afe5ff98152567438f