Update git submodules

* Update docs/submodules/yardstick from branch 'stable/euphrates'
  - nsb_installation: updates

    JIRA: YARDSTICK-500

    Change-Id: I6eef884ef6262abe49fc13bc353ca14a72a5b648
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>
    Signed-off-by: Martin Banszel <martinx.banszel@intel.com>
    Signed-off-by: Abhijit Sinha <abhijit.sinha@intel.com>
    Signed-off-by: Maciej Skrocki <maciej.skrocki@intel.com>
    (cherry picked from commit 97b961aee6653553c5a35ecee5cb766924cd10f1)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 0cb9f11..ef94db1 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 0cb9f11bb40d30d70632a7c2b1ca10a8f9f2d329
+Subproject commit ef94db1ccc5778613c231717906d0f6a2f481581