RFE: Add support for parameter inside user_data VDU property

[Martin Ivanov]

We are trying to achieve user parameter inside cloud-init user_data VDU property.
Something like this:
topology_template:
    inputs:
        someparam1:
          type: string
        someparam2:
          type: string
  ...

        VDU1:
          properties:
            ...
            user_data_format: RAW
            user_data:
              #cloud-config
              vnfparam1: { get_param: { get_input: someparam1 } }
              vnfparam2: { get_param: { get_input: someparam2 } }
            ...
          type: tosca.nodes.nfv.VDU.Tacker