Update git submodules

* Update docs/submodules/yardstick from branch 'stable/euphrates'
  - Merge "Create the ovs-vswitchd logging directory" into stable/euphrates
  - Create the ovs-vswitchd logging directory

    Change-Id: Id7f55f7fcb2fec2866b76821595776908ac30c04
    Signed-off-by: Martin Banszel <martinx.banszel@intel.com>
    (cherry picked from commit bdcae10b04debea07e4553aab6e4ce43011d5f62)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index b529585..b310586 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit b529585719b1ce0494090ec5dbb52a2be0668bb5
+Subproject commit b31058665cf345feb46c371abdfa7bb82cf12936