Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Switched to stable/euphrates for samplevnfs projext

    Change-Id: I0305c263740c25bdfa3bb2667838ca2b75d33ba0
    Signed-off-by: Maciej Skrocki <maciej.skrocki@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 578a903..24becc7 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 578a9031d8d0c6f8631db13e89856abbdf8d23d9
+Subproject commit 24becc79e0abecaaa24aa018ecac4476738e0a66