Update git submodules

* Update docs/submodules/yardstick from branch 'stable/euphrates'
  - update release notes for Euphrates 5.1.0

    Change-Id: I11b248882dd314baebd3ab4e7e676a1f3e0b50cd
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>
    (cherry picked from commit 9d0f99349d2ea4499670708aacb1569cad0389aa)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 2292505..22c3213 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 2292505e94d2225569d743c9e31063ba6bff03f8
+Subproject commit 22c32132463046ab0759295aa2f7ed840c75e253