Opencontrail plug-in implementation for core resources

Adds Opencontrail plug-in implementation with unit tests
This patch has no dependency on any other blueprints
The link below describes how to install VIF driver for opencontrail
https://github.com/Juniper/contrail-controller/wiki/
OpenContrail-bring-up-and-provisioning

- The contrail_plugin_core.py is the main interface for neutron common
  infrastructure. It relays API requests to the opencontrail controller

DocImpact
Change-Id: I501bf669b2a999a171f9a3ee3e9893d4ead50e3b
Implements: blueprint juniper-plugin-with-extensions

setup.cfg

@@ -80,6 +80,7 @@ data_files =
     etc/neutron/plugins/plumgrid = etc/neutron/plugins/plumgrid/plumgrid.ini
     etc/neutron/plugins/ryu = etc/neutron/plugins/ryu/ryu.ini
     etc/neutron/plugins/vmware = etc/neutron/plugins/vmware/nsx.ini
+    etc/neutron/plugins/opencontrail = etc/neutron/plugins/opencontrail/contrailplugin.ini
 scripts =
     bin/neutron-rootwrap
     bin/neutron-rootwrap-xen-dom0