Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "requirements.txt: add license info"
  - requirements.txt: add license info

    Change-Id: I9de6a51e7efb9e49da5bbd541c466f106c3a52e3
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index ca0aaae..c0af9d0 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit ca0aaae662da454451e1efdbef2cd3f779f7c093
+Subproject commit c0af9d0667c5653e6a1eba08c8b53664dce865f8