Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Use assertIn(x, y) instead of other variations"
  - Use assertIn(x, y) instead of other variations

    unittest.assertIn(x,y) should be used instead of:
    * unittest.assertTrue(x in y)
    * unittest.assertEqual(x in y, True)

    Also fixes pep8 violations existing in the file.

    Change-Id: I705c1bd4af74757b5c928995894aede436d66817
    JIRA: YARDSTICK-901
    Signed-off-by: Emma Foley <emma.l.foley@intel.com>