Group Policy: Resource Mapping Driver

(Patch series identifier: GPM-RMD-1)

This patch adds the resource_mapping group policy driver, which
renders group policy via mappings to traditional neutron resources,
including networks, subnets, ports, and routers. This initial version
of the driver does not yet handle policy rule resources, so all
traffic is allowed between endpoint groups that share an L3 policy.

Partially-implements: blueprint group-based-policy-abstraction

Author:            Bob Kukura <kukura@noironetworks.com>
Co-Authored-By:    Sumit Naiksatam <sumitnaiksatam@gmail.com>
Co-Authored-By:    Stephen Wong <s3wong@midokura.com>
Co-Authored-By:    Mohammad Banikazemi <mb@us.ibm.com>
Co-Authored-By:    Mandeep Dhami <dhami@noironetworks.com>

Change-Id: Ib4ca4fc9ae63f0f1295c95c01fd712ecc1ebb082