Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Add "YARD_IMG_ARCH" input variable to "build_yardstick_image.yml""
  - Add "YARD_IMG_ARCH" input variable to "build_yardstick_image.yml"

    "YARD_IMG_ARCH" variable is added as input parameter to
    "build_yardstick_image.yml" ansible script, in order to generate
    the correct image for the running architecture.

    JIRA: YARDSTICK-1058

    Change-Id: I33954c236695478eaae34fcfca2e9d5b40791bbf
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>