Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Add container pull option to install.yaml"
  - Add container pull option to install.yaml

    Supported Yardstick installation modes in yardstick.yaml: baremetal
    and container. First is used to install Yardstick on baremetal,
    another is used during docker build to install Yardstick in container.

    Added third option: 'container pull': to pull docker image
    (opnfv/yardstick) from Docker hub and start container.

    JIRA: YARDSTICK-1392

    Change-Id: I4158de3eb6fcbe0018a15fdda89a3e3ab29c26bb
    Signed-off-by: Stepan Andrushko <stepanx.andrushko@intel.com>