Classes lack metaclass decoration

Add decorations where required.

There are roughly a dozen classes in Neutron that define abstract
methods or properties but are not decorated with
@six.add_metaclass(abc.ABCMeta). Without this decoration, children
can be created without defining the required methods or properties.

Decorating RBACColumns in db/rbac_db_models.py causes failures and will
be reported separately.

Decorating unit tests is of dubious benifit and should be addressed
separately (if at all).

There are also several more places where metaclassing isn't correct, to
be taken care of in follow-on patches.

For example, BaseScheduler is using the fact the None doesn't have a
filter_agents() method, which gives developers confusing error messages
when they incorrectly implement the interface, and they won't see any
error until schedule() is called. As an aside, the docstring for this
base class is also incorrect.

Change-Id: I2b2cce37d9b0d40559a715a7d510a969b8ba9963
Closes-Bug: #1577648

neutron/agent/linux/dhcp.py

@@ -172,6 +172,7 @@ class DhcpBase(object):
         raise NotImplementedError()
 
 
+@six.add_metaclass(abc.ABCMeta)
 class DhcpLocalProcess(DhcpBase):
     PORTS = []
 

neutron/extensions/agent.py

@@ -17,6 +17,7 @@ import abc
 
 from neutron_lib.api import converters
 from neutron_lib import exceptions
+import six
 
 from neutron._i18n import _
 from neutron.api import extensions
@@ -122,6 +123,7 @@ class Agent(extensions.ExtensionDescriptor):
             return {}
 
 
+@six.add_metaclass(abc.ABCMeta)
 class AgentPluginBase(object):
     """REST API to operate the Agent.
 

neutron/extensions/dhcpagentscheduler.py

@@ -17,6 +17,7 @@ import abc
 
 from neutron_lib import constants
 from neutron_lib import exceptions
+import six
 
 from neutron._i18n import _
 from neutron.api import extensions
@@ -135,6 +136,7 @@ class NetworkNotHostedByDhcpAgent(exceptions.Conflict):
                 " by the DHCP agent %(agent_id)s.")
 
 
+@six.add_metaclass(abc.ABCMeta)
 class DhcpAgentSchedulerPluginBase(object):
     """REST API to operate the DHCP agent scheduler.
 

neutron/extensions/l3.py

@@ -18,6 +18,7 @@ import abc
 from neutron_lib.api import converters
 from neutron_lib import exceptions as nexception
 from oslo_config import cfg
+import six
 
 from neutron._i18n import _
 from neutron.api import extensions
@@ -220,6 +221,7 @@ class L3(extensions.ExtensionDescriptor):
             return {}
 
 
+@six.add_metaclass(abc.ABCMeta)
 class RouterPluginBase(object):
 
     @abc.abstractmethod

neutron/extensions/l3agentscheduler.py

@@ -18,6 +18,7 @@ import abc
 from neutron_lib import constants
 from neutron_lib import exceptions
 from oslo_log import log as logging
+import six
 import webob.exc
 
 from neutron._i18n import _, _LE
@@ -183,6 +184,7 @@ class DVRL3CannotRemoveFromDvrAgent(exceptions.Conflict):
                 "an agent in 'dvr' mode.")
 
 
+@six.add_metaclass(abc.ABCMeta)
 class L3AgentSchedulerPluginBase(object):
     """REST API to operate the l3 agent scheduler.
 

neutron/plugins/ml2/drivers/l2pop/rpc_manager/l2population_rpc.py

@@ -104,6 +104,7 @@ class L2populationRpcCallBackMixin(object):
         pass
 
 
+@six.add_metaclass(abc.ABCMeta)
 class L2populationRpcCallBackTunnelMixin(L2populationRpcCallBackMixin):
     '''Mixin class of L2-population call back for Tunnel.
 

neutron/plugins/ml2/drivers/type_tunnel.py

@@ -21,6 +21,7 @@ from oslo_config import cfg
 from oslo_db import api as oslo_db_api
 from oslo_db import exception as db_exc
 from oslo_log import log
+import six
 from six import moves
 from sqlalchemy import or_
 
@@ -45,6 +46,7 @@ def chunks(iterable, chunk_size):
         chunk = list(itertools.islice(iterator, 0, chunk_size))
 
 
+@six.add_metaclass(abc.ABCMeta)
 class TunnelTypeDriver(helpers.SegmentTypeDriver):
     """Define stable abstract interface for ML2 type drivers.
 

neutron/scheduler/base_resource_filter.py

@@ -15,7 +15,10 @@
 
 import abc
 
+import six
 
+
+@six.add_metaclass(abc.ABCMeta)
 class BaseResourceFilter(object):
     """Encapsulate logic that is specific to the resource type."""
     @abc.abstractmethod

neutron/scheduler/base_scheduler.py

@@ -17,7 +17,10 @@ import abc
 from operator import attrgetter
 import random
 
+import six
 
+
+@six.add_metaclass(abc.ABCMeta)
 class BaseScheduler(object):
     """The base scheduler (agnostic to resource type).
        Child classes of BaseScheduler must define the

neutron/tests/unit/extensions/foxinsocks.py

@@ -16,6 +16,7 @@
 import abc
 
 from oslo_serialization import jsonutils
+import six
 
 from neutron.api import extensions
 from neutron import wsgi
@@ -27,6 +28,7 @@ class FoxInSocksController(wsgi.Controller):
         return "Try to say this Mr. Knox, sir..."
 
 
+@six.add_metaclass(abc.ABCMeta)
 class FoxInSocksPluginInterface(extensions.PluginInterface):
 
     @abc.abstractmethod