Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - test_sample_vnf: mock time

    Change-Id: Id8aa734fee431d90cbdc1e0eb2173784ada822fe
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 5a756e6..f0248de 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 5a756e6171ad2d867914793dc2fd8b1aa7a19a6e
+Subproject commit f0248de2e8a6fd7e6649081a1d58648e56685a8b