ML2 provider network partial specs let admins choose some
multiprovider network attributes and let neutron choose remaining
attributes. This change provides the implementation for
multiprovider networks.
In practice, for VLAN/GRE/VXLAN segments provider:segmentation_id
choice can be delegated to neutron, in such case neutron try to find
a segment in tenant network pools which respects provided segment
attributes. For VLAN segments provider:physical_network choice can
also be delegated.
DocImpact
Implements blueprint provider-network-partial-specs
Change-Id: I1cf1441a179ec527674276b71e9924841f8570b6