Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "test_vsperf_dpdk: remove unused and incorrect mock open"
  - test_vsperf_dpdk: remove unused and incorrect mock open

    need to use create=True with mock open anyway

    Change-Id: I3a35688cf8c367434db9d0cf057030d49deddd0d
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 4de16cb..e71da0a 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 4de16cbc3c7a4e03542c6256f3aeda79dbf49b62
+Subproject commit e71da0adfe3fae77311d7a75c5a74b87dfa0890e