vCloud host-pooling

This PR enabled the use of "pooling_api" configuration parameter:

    HOSTS:
      debian-7-x86-64:
        roles:
          - master
        platform: debian-7-x86_64
        template: Delivery/Quality Assurance/Templates/vCloud/debian-7-x86_64
        hypervisor: vcloud
    CONFIG:
      nfs_server: none
      consoleport: 443
      pooling_api: http://vcloud.delivery.puppetlabs.net/
      datastore: instance0
      folder: Delivery/Quality Assurance/Staging/Dynamic
      resourcepool: delivery/Quality Assurance/Staging/Dynamic

If pooling_api is found, it will select an already-provisioned VM and run tests on it instead of dynamically provisioning a new host.