Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Modify the Docker diff file for ARM64"
  - Modify the Docker diff file for ARM64

    In I5d9e135449b2d35f051ecf5fa63a1ce11030de4a the Dockerfile was modified.
    Until we can handle the Dockerfile generation for each architecture in a
    better way, we need to keep updated the Docker diff file for ARM64.

    JIRA: YARDSTICK-1030

    Change-Id: Ibd9224dcb9a7a897b0da8aab126f62983b5e70bd
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>