Remove usage of Neutron's MechanismDriverError

The upstream plugin will catch any exception, so there is not need to
import this exception from Neutron. We can raise our specific exception
and remove this dependency.

Change-Id: I6df50480eef474511fe18a8b7c6d5d0d1afb666b

networking_arista/ml2/mechanism_arista.py

@@ -19,9 +19,9 @@ from neutron_lib.api.definitions import portbindings
 from neutron_lib import constants as n_const
 from oslo_config import cfg
 from oslo_log import log as logging
+from oslo_utils import excutils
 
 from neutron.common import constants as neutron_const
-from neutron.plugins.ml2.common import exceptions as ml2_exc
 from neutron.plugins.ml2 import driver_api
 
 from networking_arista._i18n import _, _LI, _LE
@@ -716,9 +716,8 @@ class AristaDriver(driver_api.MechanismDriver):
                         tenant_id, network_id,
                         context.network.current['name'], all_segments)
                 except arista_exc.AristaRpcError:
-                    LOG.error(_LE("Failed to create network segments"))
-                    raise ml2_exc.MechanismDriverError(
-                        method='update_port_postcommit')
+                    with excutils.save_and_reraise_exception():
+                        LOG.error(_LE("Failed to create network segments"))
 
             try:
                 orig_host = context.original_host
@@ -729,16 +728,11 @@ class AristaDriver(driver_api.MechanismDriver):
 
                 if orig_host and (port_down or host != orig_host or
                    device_id == neutron_const.DEVICE_ID_RESERVED_DHCP_PORT):
-                    try:
-                        LOG.info("Deleting the port %s" % str(orig_port))
-                        # The port moved to a different host or the VM
-                        # connected to the port was deleted or its in DOWN
-                        # state. So delete the old port on the old host.
-                        self._delete_port(orig_port, orig_host, tenant_id)
-                    except ml2_exc.MechanismDriverError:
-                        # If deleting a port fails, then not much can be done
-                        # about it. Log a warning and move on.
-                        LOG.warning(UNABLE_TO_DELETE_PORT_MSG)
+                    LOG.info("Deleting the port %s" % str(orig_port))
+                    # The port moved to a different host or the VM
+                    # connected to the port was deleted or its in DOWN
+                    # state. So delete the old port on the old host.
+                    self._delete_port(orig_port, orig_host, tenant_id)
                 if(port_provisioned and net_provisioned and hostname and
                    is_vm_boot and not port_down and
                    device_id != neutron_const.DEVICE_ID_RESERVED_DHCP_PORT):
@@ -800,7 +794,7 @@ class AristaDriver(driver_api.MechanismDriver):
             try:
                 self._delete_port(port, host, tenant_id)
                 self._delete_segment(context, tenant_id)
-            except ml2_exc.MechanismDriverError:
+            except arista_exc.AristaRpcError:
                 # Can't do much if deleting a port failed.
                 # Log a warning and continue.
                 LOG.warning(UNABLE_TO_DELETE_PORT_MSG)
@@ -955,8 +949,8 @@ class AristaDriver(driver_api.MechanismDriver):
             try:
                 self.rpc.delete_tenant(tenant_id)
             except arista_exc.AristaRpcError:
-                LOG.info(EOS_UNREACHABLE_MSG)
-                raise ml2_exc.MechanismDriverError(method='delete_tenant')
+                with excutils.save_and_reraise_exception():
+                    LOG.info(EOS_UNREACHABLE_MSG)
 
     def _host_name(self, hostname):
         fqdns_used = cfg.CONF.ml2_arista['use_fqdn']