Improve Networking-related Options

[aznashwan]

Allow users to more granularly select networking-related options for Migrated/Replicated by adding a new networking_options parameter to the Migrations/Replicas APIs.

The options in the payload should include (but is not limited to) the following example:

{
  "networking_options": {
    "instance_name_or_id": {
      // applied to all NICs by default
      "dhcp_configuration": "enum(USE_DHCP | USE_STATIC_IPS | IGNORE)",  
      "nic_options": [{
        "id": "<ID of NIC, can optionally be its MAC>",
        "mapped_network": "<identifier of mapped network>",
        "dhcp_configuration": "enum(USE_DHCP | USE_STATIC_IPS | IGNORE)",
        // NOTE: some platforms allow for assigning an IP from the platform-level
        //  to the VM. For those which don't, using dhcp_configuration=USE_DHCP
        // with 'new_ip_address' will not be allowed.
        "new_ip_address": "<optional new IP address to set the NIC>",
        "new_mac_address": "<optional_new_MAC_address>",
        "associate_public_ip": true,
        // NOTE: only required if 'associate_public_ip'=True
        "public_network_identifier": "<ID of public network to associate PIP from"
      },
      {
        "id": ...
      }]
    }
  }
}

These will be passed directly to both the OSMorphing tools during the set_net_config() call, as well as the providers themselves.

[aznashwan]

Partially addressed by #50, new options still need adding though,