Add stronger checking of backend configuration

Set a default if the backend configuration is not
provided as well as check for the configuration
being a dictionary instead of any arbitary non-false
type.

Change-Id: Id458ac0eb2d7b86c5602ed2f23a52fb2c6f6f0e7

taskflow/persistence/backends/base.py

@@ -26,6 +26,11 @@ class Backend(object):
     """Base class for persistence backends."""
 
     def __init__(self, conf):
+        if not conf:
+            conf = {}
+        if not isinstance(conf, dict):
+            raise TypeError("Configuration dictionary expected not: %s"
+                            % type(conf))
         self._conf = conf
 
     @abc.abstractmethod