Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Vincenzo stepping down as Yardstick committer"
  - Vincenzo stepping down as Yardstick committer

    From: opnfv-tech-discuss-bounces@lists.opnfv.org [mailto:opnfv-tech-discuss-bounces@lists.opnfv.org] On Behalf Of Riccobene, Vincenzo M
    Sent: Thursday, January 18, 2018 2:35 AM
    To: opnfv-tech-discuss@lists.opnfv.org
    Subject: [opnfv-tech-discuss] Stepping down as Yardstick committer

    Hello,
    I am currently a committer for the OPNFV Yardstick project, but as I see unfortunately in the last months I have been absent from the project since other commitments took higher priorities and all my time, resulting in no major contributions to Yardstick, and I consequently decided to step down from the positon of committer.

    It has been a great pleasure to contribute to the community and I hope I will be able to contribute again in the future.
    Thank you very much all!

    Best Regards.
    Vince

    Change-Id: I809021b4081caddb60549204a742b93134190a87
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>