All classes should explicitly inherit object class

To avoid pylint errors six.with_metaclass was substituted
with six.add_metaclass and explicit inheritance of object class.

Change-Id: I516f111a9ba1af414b1a5daefad44b743af0412f

taskflow/engines/action_engine/base_action.py

@@ -22,7 +22,8 @@ import abc
 import six
 
 
-class Action(six.with_metaclass(abc.ABCMeta)):
+@six.add_metaclass(abc.ABCMeta)
+class Action(object):
     """Base action class"""
 
     @abc.abstractmethod

taskflow/engines/base.py

@@ -22,7 +22,8 @@ import abc
 import six
 
 
-class EngineBase(six.with_metaclass(abc.ABCMeta)):
+@six.add_metaclass(abc.ABCMeta)
+class EngineBase(object):
     """Base for all engines implementations"""
 
     def __init__(self, flow, flow_detail, backend, conf):

taskflow/flow.py

@@ -22,7 +22,8 @@ import six
 from taskflow.utils import reflection
 
 
-class Flow(six.with_metaclass(abc.ABCMeta)):
+@six.add_metaclass(abc.ABCMeta)
+class Flow(object):
     """The base abstract class of all flow implementations.
 
     A flow is a structure that defines relationships between tasks. You can

taskflow/jobs/jobboard.py

@@ -22,7 +22,8 @@ import abc
 import six
 
 
-class JobBoard(six.with_metaclass(abc.ABCMeta)):
+@six.add_metaclass(abc.ABCMeta)
+class JobBoard(object):
     """A jobboard is an abstract representation of a place where jobs
     can be posted, reposted, claimed and transferred. There can be multiple
     implementations of this job board, depending on the desired semantics and

taskflow/listeners/base.py

@@ -33,7 +33,8 @@ LOG = logging.getLogger(__name__)
 FINISH_STATES = (states.FAILURE, states.SUCCESS)
 
 
-class LoggingBase(six.with_metaclass(abc.ABCMeta)):
+@six.add_metaclass(abc.ABCMeta)
+class LoggingBase(object):
     """This provides a simple listener that can be attached to an engine which
     can be derived from to log the received actions to some logging backend. It
     provides a useful context manager access to be able to register and

taskflow/persistence/backends/base.py

@@ -21,7 +21,8 @@ import abc
 import six
 
 
-class Backend(six.with_metaclass(abc.ABCMeta)):
+@six.add_metaclass(abc.ABCMeta)
+class Backend(object):
     """Base class for persistence backends."""
 
     def __init__(self, conf):
@@ -38,7 +39,8 @@ class Backend(six.with_metaclass(abc.ABCMeta)):
         pass
 
 
-class Connection(six.with_metaclass(abc.ABCMeta)):
+@six.add_metaclass(abc.ABCMeta)
+class Connection(object):
     """Base class for backend connections."""
 
     @abc.abstractproperty

taskflow/storage.py

@@ -393,5 +393,6 @@ class Storage(object):
         return state
 
 
-class ThreadSafeStorage(six.with_metaclass(tu.ThreadSafeMeta, Storage)):
+@six.add_metaclass(tu.ThreadSafeMeta)
+class ThreadSafeStorage(Storage):
     pass

taskflow/task.py

@@ -108,7 +108,8 @@ def _build_arg_mapping(task_name, reqs, rebind_args, function, do_infer):
     return result
 
 
-class BaseTask(six.with_metaclass(abc.ABCMeta)):
+@six.add_metaclass(abc.ABCMeta)
+class BaseTask(object):
     """An abstraction that defines a potential piece of work that can be
     applied and can be reverted to undo the work as a single unit.
     """