Update git submodules

* Update docs/submodules/yardstick from branch 'stable/fraser'
  - nsb_setup: pin docker image version to release tag

    The install scripts pull tags for stable releases.

    We need to temporarily pin the image tag to the unreleased tag
    because we have to update the code before we actually tag the image.

    Or maybe we should make this a parameter to the script

    JIRA: YARDSTICK-1137

    Change-Id: I2e5f13ffe19d1c19fd7b8e071df28fd225be3d79
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 26083c4..5a18f54 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 26083c4931c0bc72569d782c9df569dc6369077b
+Subproject commit 5a18f5420f9077557d9f50ebe420b66813ebee49