Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Make 'Scenario' classes plugable"
  - Make 'Scenario' classes plugable

    This patch makes yardstick.benchmark.scenario.base:Scenario classes
    plugable.

    A new entry point is added to the setup. This entry point could be
    extended in other plugin projects to add new Scenario classes.

    E.g.: take a look at [1]. This is a Yardstick plugin example project.
    Clone the project and execute, from the project directory:

      $ sudo -EH python setup.py install

    This will add a new module to python ('yardstick-new-plugin') and a
    new Scenario class.

    Now list the scenarios in Yardstick:

      $ yardstick scenario list
        ...
        | SpecCPU2006_for_VM    | Spec CPU2006 benchmark for Virtual Machine |
        | SpecCPU2006           | Spec CPU2006 benchmark                     |
        | Dummy2                | Execute Dummy (v2!) echo                   |
        +-----------------------+--------------------------------------------+

    [1] https://github.com/ralonsoh/yardstick_new_plugin

    JIRA: YARDSTICK-910

    Change-Id: Ib70ee9bf4dc7ff91d1dd6377317b313288e36bff
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>