Add ability to create provider networks (vlan,flat).

Provider network map directly to an existing physical network in
a data center. It's routable by default. Neutron v2.0 API implements
it using Provider Networks Neutron API Extension. This is different
from tenant network(implemented by 'OS::Neutron::Net'resource) and has
different requirements.

This ('OS::Neutron::ProviderNet') resource leverages additional
attributes as listed below from Neutron API extension.

provider:network_type - Specifies the nature of the physical network
mapped to this network resource. Examples are flat and vlan.

provider:physical_network - Identifies the physical network on top of
which this network object is being implemented.

provider:segmentation_id - Identifies an isolated segment on the
physical network.

Change-Id: Ic085d13c866722b0e6ed9fd7a4f43dd92d5b1a0b
Implements: blueprint neutron-net-resource-add-provider-network
Merge "Add ability to create provider networks (vlan,flat)."