Remove the base postfix for engine abstract base class

Remove the non-standard pattern of calling the engine
base class EngineBase; since it's already obvious that
its a base class by it existing in the base engine
module.

Change-Id: Ia146ec6541ee96aa6a78fa659267d2a69e3b9e97

taskflow/engines/action_engine/engine.py

@@ -42,7 +42,7 @@ def _start_stop(executor):
         executor.stop()
 
 
-class ActionEngine(base.EngineBase):
+class ActionEngine(base.Engine):
     """Generic action-based engine.
 
     This engine compiles the flow (and any subflows) into a compilation unit

taskflow/engines/base.py

@@ -25,7 +25,7 @@ from taskflow.utils import misc
 
 
 @six.add_metaclass(abc.ABCMeta)
-class EngineBase(object):
+class Engine(object):
     """Base for all engines implementations.
 
     :ivar notifier: A notification object that will dispatch events that