Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Heat: support create and attach volume in heat type context

    JIRA: YARDSTICK-756

    Some test scenarios require VM with volume attached.
    This work is about supporting create and attach volume in heat type context.

    context:
      name: demo
      image: cirros-0.3.5
      flavor: yardstick-flavor
      user: cirros

      placement_groups:
        pgrp1:
          policy: "availability"

      servers:
        athena:
          floating_ip: true
          # per-vm inline volume definition. if no volume size specified, then this
          # volume should be an existing volume in the openstack environment
          volume: yardstick-volume
          placement: "pgrp1"
        ares:
          # per-vm inline volume definition. if volume size is specified, then this
          # volume will be crated and attach to the vm
          volume:
            name: test-volume
            size: 10
          # volume mountpoint is also configurable
          volume_mountpoint: /dev/vdb
          placement: "pgrp1"

      networks:
        test:
          cidr: '10.0.1.0/24'

    Change-Id: Ief87b313980a59eac229eb4780d93ffc929ceb66
    Signed-off-by: JingLu5 <lvjing5@huawei.com>