Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Update Dockerfile.aarch64.patch"
  - Update Dockerfile.aarch64.patch

    The docker image was not built for aarch64 due to recent changes in the
    Dockerfile. The updates to the Dockerfile.aarch64.patch are:
    - update docker version to 16.04
    - install dependencies for pyopenssl==17.5.0 (libssl-dev and libffi-dev)

    JIRA: ARMBAND-353

    Change-Id: I915172d4e7ce21b1f5de044b20301b076cb6fe20
    Signed-off-by: Cristina Pauna <cristina.pauna@enea.com>