Tenant networking support for Ironic driver

This blueprint covers changes needed for tenant network support for Ironic.

Currently, Ironic only works on a flat network shared between control plane and tenants. There's an ongoing effort to allow for arbitrary networks to be connected to Ironic nodes in various configurations:
https://blueprints.launchpad.net/ironic/+spec/network-provider
https://blueprints.launchpad.net/ironic/+spec/ironic-ml2-integration

There are changes that need to be made to Nova to support this. Specifically:

* The port-create calls to Neutron need to be made with a null binding:host_id. This signals to Neutron that it shouldn't bind the port yet. To keep the provisioning process away from the tenant network, we need to wait for the deployment to complete before binding the port, which only Ironic can control. After completing the deployment, Ironic will make a port-update call with: 1) a binding:host_id value of "baremetal:$node_uuid", and 2) physical switchport information necessary to connect the port.

* The ironic driver will need updates to be able to handle Ironic's "port groups" as well as "ports". A port group is a single logical connection comprised of multiple physical NICs; used in LAG and MLAG configurations.

* A BAREMETAL vnic type will be added to support the BAREMETAL vnic type that was previously added in Neutron.

This will support the basic tenant networking support we've built out in Ironic; some thought should be put into the future of this integration. For example, in the future we'll want to support multiple networks via VLAN or VXLAN over a pair of bonded NICs (currently Nova enforces a 1:1 mapping of NICs to networks, as in the virtual world NICs can be created on the fly).