Update git submodules

* Update docs/submodules/yardstick from branch 'stable/euphrates'
  - fix random test_task unittest fail due to os.environ mock

    sometime Jenkins fails due to what I guess are concurrency problems
    in os.environ mock

    ======================================================================
    FAIL: tests.unit.benchmark.core.test_task.TaskTestCase.test_parse_suite_with_constraint_no_args
    tags: worker-10
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "/usr/lib/python3.5/unittest/mock.py", line 1157, in patched
        return func(*args, **keywargs)
      File "/home/jenkins/opnfv/slave_root/workspace/yardstick-verify-euphrates/tests/unit/benchmark/core/test_task.py", line 208, in test_parse_suite_with_constraint_no_args
        task_files, task_args, task_args_fnames = t.parse_suite()
      File "/home/jenkins/opnfv/slave_root/workspace/yardstick-verify-euphrates/yardstick/benchmark/core/task.py", line 455, in parse_suite
        cur_pod = os.environ.get('NODE_NAME', None)
      File "/usr/lib/python3.5/unittest/mock.py", line 917, in __call__
        return _mock_self._mock_call(*args, **kwargs)
      File "/usr/lib/python3.5/unittest/mock.py", line 976, in _mock_call
        result = next(effect)
    StopIteration
    Ran 1262 tests in 2.375s
    FAILED (id=0, failures=1)
    error: testr failed (1)
    + testr failing

    Replace the mock decorator with a context manager to try to
    reduce the scope and duration of the mock.

    Change-Id: I342fe6c403e66c53ac4c39fd88fa9047cdfae5d9
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>
    (cherry picked from commit 2fadf7aec9e2761c39d29d8af1ee7d69d154652d)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 8386355..8c182f5 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 83863550224b960cf1abe47bf3d28533bce98027
+Subproject commit 8c182f5ff58afcee62dc25a40f3859409d2d7fb2