Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - ssh: fix unittest race condition

    os.stat is being called multiple times for some reason

    we only care that is it called at some point.

    ======================================================================
    FAIL: tests.unit.test_ssh.SSHRunTestCase.test__put_file_sftp
    tags: worker-1
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "/home/jenkins/opnfv/slave_root/workspace/yardstick-verify-master/.tox/py3/lib/python3.5/site-packages/mock/mock.py", line 1305, in patched
        return func(*args, **keywargs)
      File "/home/jenkins/opnfv/slave_root/workspace/yardstick-verify-master/tests/unit/test_ssh.py", line 458, in test__put_file_sftp
        mock_stat.assert_called_once_with("localfile")
      File "/home/jenkins/opnfv/slave_root/workspace/yardstick-verify-master/.tox/py3/lib/python3.5/site-packages/mock/mock.py", line 947, in assert_called_once_with
        raise AssertionError(msg)
    AssertionError: Expected 'stat' to be called once. Called 3 times.
    Ran 1209 tests in 2.618s
    FAILED (id=0, failures=1)
    error: testr failed (1)
    + testr failing
    ======================================================================
    FAIL: tests.unit.test_ssh.SSHRunTestCase.test__put_file_sftp
    tags: worker-1
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "/home/jenkins/opnfv/slave_root/workspace/yardstick-verify-master/.tox/py3/lib/python3.5/site-packages/mock/mock.py", line 1305, in patched
        return func(*args, **keywargs)
      File "/home/jenkins/opnfv/slave_root/workspace/yardstick-verify-master/tests/unit/test_ssh.py", line 458, in test__put_file_sftp
        mock_stat.assert_called_once_with("localfile")
      File "/home/jenkins/opnfv/slave_root/workspace/yardstick-verify-master/.tox/py3/lib/python3.5/site-packages/mock/mock.py", line 947, in assert_called_once_with
        raise AssertionError(msg)
    AssertionError: Expected 'stat' to be called once. Called 3 times.
    Ran 1 tests in 0.110s
    FAILED (id=0, failures=1)

    Change-Id: I73370996e6e0543419eec8ecbe81be424ec15822
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 6fd861c..e9d991a 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 6fd861c845a42d6a1aae8adc7facc28fba6cac58
+Subproject commit e9d991a22270cd78485dcc6c8f3ddbf70a62286b