Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "test_pktgen_dpdk_throughput: speedup unittest, mock time.sleep()"
  - test_pktgen_dpdk_throughput: speedup unittest, mock time.sleep()

    Change-Id: I74bbdee1a503ef9bad32db7d4444921f6730f465
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 7b4f2bd..8cee055 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 7b4f2bdb386eacd62f4f8e9e67d0c826adccc3b0
+Subproject commit 8cee055d67f9d1e346361ab810dcfc24f0b9ccbc