Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - [docs] Update on Yardstick installation

    Added details how to install Yardstick using install.yaml.

    Updated:
     - 04-installation.rst
     - 13-nsb-installation.rst

    JIRA: YARDSTICK-1335

    Change-Id: I526c328f1b197833a2cf496cfef15ba89c11fab1
    Signed-off-by: Stepan Andrushko <stepanx.andrushko@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 00d4ec0..a5021a1 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 00d4ec0cdb63eddfe769de24ed096d795e0dd00b
+Subproject commit a5021a12cdce9f68ff15eb0f1d8d30204081bacc