Arista ML2 mechanism driver clean up and integration with port binding

fixes bug: 1215097

This patch addresses minor cleanups and integration with port binding
and dhcp support into Arista ML2 mechanism driver.

Change-Id: Icebc4aa1c57278171cc6b5209107b8eab833249c

neutron/db/migration/alembic_migrations/versions/14f24494ca31_arista_ml2.py

@@ -56,7 +56,7 @@ def upgrade(active_plugins=None, options=None):
         'arista_provisioned_vms',
         sa.Column('tenant_id', sa.String(length=255), nullable=True),
         sa.Column('id', sa.String(length=36), nullable=False),
-        sa.Column('vm_id', sa.String(length=36), nullable=True),
+        sa.Column('vm_id', sa.String(length=255), nullable=True),
         sa.Column('host_id', sa.String(length=255), nullable=True),
         sa.Column('port_id', sa.String(length=36), nullable=True),
         sa.Column('network_id', sa.String(length=36), nullable=True),

neutron/plugins/ml2/drivers/mech_arista/db.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2013 OpenStack, LLC.
+# Copyright (c) 2013 OpenStack Foundation
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -55,7 +55,7 @@ class AristaProvisionedVms(model_base.BASEV2, models_v2.HasId,
     """
     __tablename__ = 'arista_provisioned_vms'
 
-    vm_id = sa.Column(sa.String(UUID_LEN))
+    vm_id = sa.Column(sa.String(STR_LEN))
     host_id = sa.Column(sa.String(STR_LEN))
     port_id = sa.Column(sa.String(UUID_LEN))
     network_id = sa.Column(sa.String(UUID_LEN))