Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "ansible image build improvement"
  - ansible image build improvement

    JIRA: YARDSTICK-879

    Add some image build vars
    Add automatic image build of nsb
    yardstick_image: ansible-playbook -e img_property="normal" -vvv -i inventory.ini build_yardstick_image.yml

    nsb_image_build: ansible-playbook -e img_property="nsb" -vvv -i inventory.ini build_yardstick_image.yml

    prepare for yardstick image uploading

    Change-Id: I9fdf30084511ca9a008df3b53887b06273bbd549
    Signed-off-by: Ace Lee <liyin11@huawei.com>