Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Heat: support vnic_type in heat type context

    JIRA: YARDSTICK-757

    Some test scenarios require VM with specific vnic type.
    This work is about supporting using different vnic types 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
          placement: "pgrp1"
        ares:
          placement: "pgrp1"

      networks:
        test:
          cidr: '10.0.1.0/24'
          vnic_type: "normal"

    Change-Id: Ia229fda72f47b04288ea107e2d58fd3e8ac91dd9
    Signed-off-by: JingLu5 <lvjing5@huawei.com>