Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Clean unit tests in "benchmark.scenarios.lib.test_create_volume.py"
  - Clean unit tests in "benchmark.scenarios.lib.test_create_volume.py

    * Use mock_object.assert_called_with instead of
        self.assertTrue(mock_object.called)
    * Remove an unneeded if clause in CreateVolume
    * Add individual tests for each method in CreateVolume

    Change-Id: I54cc56434d316f059b3822879145e6a299866fcb
    Signed-off-by: Emma Foley <emma.l.foley@intel.com>