Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Change assert statements to raises in CheckValue"
  - Change assert statements to raises in CheckValue

    * Instead of using assert statements, raise a custom exception.
    * Modify the unit tests so that they do not test unused parameters for
      equality.
    * Fix pylint and pep8 errors.

    JIRA: YARDSTICK-966

    Change-Id: I41e13a5a22086827792eaf9de8da2e4ed6dd42de
    Signed-off-by: Miikka Koistinen <miikka.koistinen@nokia.com>