Heat: support create and attach volume in heat type context

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>