Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Enforce pip version during installation"
  - Enforce pip version during installation

    Currently there is a reported problem in pip library [1]. To avoid this
    problem, the pip version should be enforced during the installation.

    [1]https://github.com/pypa/pip/issues/5079

    JIRA: YARDSTICK-1087

    Change-Id: I2ee28749f146cd3b0e1bf4ed92b51cbe6db8b2f3
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index a854a1d..e345f47 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit a854a1dde960b630c0c0d854dee9232e4c4e9ac8
+Subproject commit e345f4757abda2e7e734d86d89024d7af6e17de9