Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "vPE Sample VNF is missing in the installation scripts"
  - vPE Sample VNF is missing in the installation scripts

    Sample VNF vPE is missing in the installation scripts and should be added
    to support the execution of the test cases related.

    JIRA: YARDSTICK-1187

    Change-Id: I6684304cc97fd3bde90ca06f5fe8df9e1d11ce18
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 43eb5e0..24c73d5 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 43eb5e0b4a03278b12c002ff5a5d1c6f58da35d6
+Subproject commit 24c73d56563e2057c381af9c65ed005d1970f28a