Update git submodules

* Update docs/submodules/yardstick from branch 'stable/euphrates'
  - Merge "Adding sample trex example" into stable/euphrates
  - Adding sample trex example

    Change-Id: I3b79d33dba5cc559634122a135ff469f054214fc
    Signed-off-by: Deepak S <deepak.s@linux.intel.com>
    (cherry picked from commit 255a77da00dd047ee0c5ab1e849cf7e6ce75ecf6)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 9cf89a0..b3ebb05 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 9cf89a084b3f5840f6085aedc76ed93be8b5aec6
+Subproject commit b3ebb0526501cba14055e00ee16606f85f6212eb