Arista ML2 mech driver cleanup and integration with portbindings

fixes bug: 1215097

This patch addresses minor cleanups which are the diff between the
original version of the patch which was merged into havana master
branch and the patch that is submitted for merge into stable/havana.

The original patch that was merged into havana master branch is at:
https://review.openstack.org/#/c/49086/
The new patch which has been submitted as havana-backport-potential is:
https://review.openstack.org/#/c/54447/

This whole excercise came into play because the original patch was not
picked up in havana-rc2 because of missing tag in the bug. Therefore, the
need to submit new patch against stable/havana.

When the new patch was submitted for havana-backport-potential, few very
minor previously commented cleanups were incorporated as well. This
patch brings these minor cleanups into master branch as well. Therefore,
merge of these two patches will bring both master branch and
stable/havana at parity.

Change-Id: I4ec5273c26a27ca52b430a6c7485a44e880a1787

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

@@ -18,6 +18,8 @@
 import jsonrpclib
 from oslo.config import cfg
 
+from neutron.common import constants as n_const
+from neutron.extensions import portbindings
 from neutron.openstack.common import log as logging
 from neutron.plugins.ml2.common import exceptions as ml2_exc
 from neutron.plugins.ml2 import driver_api
@@ -73,7 +75,7 @@ def plug_port_into_network(self, vm_id, host_id, port_id,
         :param port_name: Name of the port - for display purposes
         :param device_owner: Device owner - e.g. compute or network:dhcp
         """
-        if device_owner == 'network:dhcp':
+        if device_owner == n_const.DEVICE_OWNER_DHCP:
             self.plug_dhcp_port_into_network(vm_id,
                                              host_id,
                                              port_id,
@@ -263,8 +265,8 @@ def _register_with_eos(self):
         """
         cmds = ['auth url %s user %s password %s' %
                 (self._keystone_url(),
-                 self.keystone_conf.admin_user,
-                 self.keystone_conf.admin_password)]
+                self.keystone_conf.admin_user,
+                self.keystone_conf.admin_password)]
 
         self._run_openstack_cmds(cmds)
 
@@ -609,7 +611,7 @@ def create_port_precommit(self, context):
         port = context.current
         device_id = port['device_id']
         device_owner = port['device_owner']
-        host = port['binding:host_id']
+        host = port[portbindings.HOST_ID]
 
         # device_id and device_owner are set on VM boot
         is_vm_boot = device_id and device_owner
@@ -630,7 +632,7 @@ def create_port_postcommit(self, context):
         port = context.current
         device_id = port['device_id']
         device_owner = port['device_owner']
-        host = port['binding:host_id']
+        host = port[portbindings.HOST_ID]
 
         # device_id and device_owner are set on VM boot
         is_vm_boot = device_id and device_owner
@@ -666,8 +668,9 @@ def create_port_postcommit(self, context):
                     LOG.info(msg)
 
     def update_port_precommit(self, context):
-        """At the moment we only support port name change.
+        """Update the name of a given port.
 
+        At the moment we only support port name change.
         Any other change to port is not supported at this time.
         We do not store the port names, therefore, no DB store
         action is performed here.
@@ -679,8 +682,9 @@ def update_port_precommit(self, context):
             LOG.info(msg)
 
     def update_port_postcommit(self, context):
-        """At the moment we only support port name change
+        """Update the name of a given port in EOS.
 
+        At the moment we only support port name change
         Any other change to port is not supported at this time.
         """
         port = context.current
@@ -691,7 +695,7 @@ def update_port_postcommit(self, context):
 
         device_id = port['device_id']
         device_owner = port['device_owner']
-        host = port['binding:host_id']
+        host = port[portbindings.HOST_ID]
         is_vm_boot = device_id and device_owner
 
         if host and is_vm_boot:
@@ -732,7 +736,7 @@ def delete_port_precommit(self, context):
         """Delete information about a VM and host from the DB."""
         port = context.current
 
-        host_id = port['binding:host_id']
+        host_id = port[portbindings.HOST_ID]
         device_id = port['device_id']
         tenant_id = port['tenant_id']
         network_id = port['network_id']
@@ -753,7 +757,7 @@ def delete_port_postcommit(self, context):
         """
         port = context.current
         device_id = port['device_id']
-        host = port['binding:host_id']
+        host = port[portbindings.HOST_ID]
         port_id = port['id']
         network_id = port['network_id']
         tenant_id = port['tenant_id']
@@ -762,7 +766,7 @@ def delete_port_postcommit(self, context):
         try:
             with self.eos_sync_lock:
                 hostname = self._host_name(host)
-                if device_owner == 'network:dhcp':
+                if device_owner == n_const.DEVICE_OWNER_DHCP:
                     self.rpc.unplug_dhcp_port_from_network(device_id,
                                                            hostname,
                                                            port_id,