Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Proposing Abhijit Sinha as a committer in Yardstick"
  - Proposing Abhijit Sinha as a committer in Yardstick

    Abhijit Sinha has contributed to the Yardstick project in many ways
    Achievements/Contributions include:
    - PROX VNF and TG for NFVi characterization tests
    - Attending Yardstick meetings
    - PROX Grafanfa dashboards

    Change-Id: I455ff22b8cb68c6422fc864659668412bed3e9c4
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>