VCNS driver implementation

Implement API/driver interface for configuring vShield Edge Appliance.

Currently implemented functions:
    - Deploy an Edge
    - Destroy an Edge
    - Configuring interfaces
    - Configuring SNAT/DNAT rules
    - Configuring default gateway and static routes
    - Query Edge status
    - Task-based asynchronous model
    - Allow old routes/nat config to be skipped if new updates are coming

Implements: blueprint vcns-driver
Change-Id: I881bde907f4c90de4c919d008b76b8c2a2d0e1fd

etc/neutron/plugins/nicira/nvp.ini

@@ -134,3 +134,34 @@
 # that using the minimum chunk size will cause the interval between two
 # requests to be less than min_sync_req_delay
 # min_chunk_size = 500
+
+[vcns]
+# URL for VCNS manager
+# manager_uri = https://management_ip
+
+# User name for VCNS manager
+# user = admin
+
+# Password for VCNS manager
+# password = default
+
+# (Optional) Datacenter ID for Edge deployment
+# datacenter_moid =
+
+# (Optional) Deployment Container ID for NSX Edge deployment
+# If not specified, either a default global container will be used, or
+# the resource pool and datastore specified below will be used
+# deployment_container_id =
+
+# (Optional) Resource pool ID for NSX Edge deployment
+# resource_pool_id =
+
+# (Optional) Datastore ID for NSX Edge deployment
+# datastore_id =
+
+# (Required) UUID of logic switch for physical network connectivity
+# external_network =
+
+# (Optional) Asynchronous task status check interval
+# default is 2000 (millisecond)
+# task_status_check_interval = 2000