Nailgun should serialize SR-IOV related info into astute.yaml

When end user configures interface as SR-IOV and use it for Private network:

* Network transformations should add port using `add-port` action with provider
  `sriov` and fill vendor_specific attributes as following. If sriov ports
  are not presented in transformations it means that SR-IOV is not enabled for
  this node (because no interfaces will be set up).

* Cluster-wide parameter `supported_pci_vendor_devs` will be generated and
  contains PCI-ID of NIC virtual functions from all interfaces where user
  enabled SR-IOV. If this parameter is empty, it means SR-IOV is not enabled at
  all.

* Custom kernel boot line should be passed to SR-IOV enabled nodes.

According to this, astute.yaml will be extended and looks like this

::

  network_scheme:
    transformations:
    - action: add-port
      name: enp1s0f0
      provider: sriov
      vendor_specific:
        sriov_numvfs: <NUM>
        physnet: physnet2
  quantum_settings:
    supported_pci_vendor_devs:
      - <PCI-ID>

where <NUM> is number and <PCI-ID> is string like "8086:1515".