Group Policy CLI-1: EP, EPG, L2 Policy, L3 Policy

This patch includes Neutronclient (CLI) support for GP Endpoint, Endpoint Group, L2 Policy, L3 Policy resources.

Change-Id: I44acc6a6b340e931f7540794bbc929c426d1d2cc
Partially-implements: blueprint group-based-policy-abstraction
Group Policy CLI-2: Classifiers, Actions, and Rules

This patch includes Neutron client support for Classifiers, Actions and Rules resources.

Change-Id: Ieddb76835f57cbfa77fdbc81ee4a84d3803de902
Partially-implements: blueprint group-based-policy-abstraction
Group Policy CLI-3: Contracts

This patch includes Neutron client support for Contracts.

Change-Id: Ibf26a818030f80d7e8de2f9f0c03f2074bca2561
Partially-implements: blueprint group-based-policy-abstraction