Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Change nsb_setup.sh to use NSB image instead of raw"
  - Change nsb_setup.sh to use NSB image instead of raw

    The `ansible/roles/create_samplevnfs_image/tasks/main.yml` ansible role
    uses raw NSB image (yardstick-xenial-server.raw) to upload it to
    OpenStack instead QCOW2 NSB converted image (yardstick-nsb-image.img
    which is converted from the raw). Changed the create_samplevnfs_image
    role to to use NSB image.

    JIRA: YARDSTICK-1000

    Change-Id: Ieda9f14e6882ca854331b4eccc9a4cb390b6a475
    Signed-off-by: Mytnyk, Volodymyr <volodymyrx.mytnyk@intel.com>