user friendly reporting of config errors

Config errors are collected first, and raised after processing
all modules. This is more user friendly.

+ remove redundant check for predefined accessibles in modules.py
+ fixed error handling for exporting parameters in params.py
+ fixed handling of bare attributes overwriting properties

Change-Id: I894bda291ab85ccec3d771c4903393c808af0a2a

secop/properties.py

@@ -179,7 +179,7 @@ class HasProperties(HasDescriptors):
             if po.mandatory:
                 try:
                     self.propertyValues[pn] = po.datatype(self.propertyValues[pn])
-                except (KeyError, BadValueError) as e:
+                except (KeyError, BadValueError):
                     name = getattr(self, 'name', self.__class__.__name__)
                     raise ConfigError('%s.%s needs a value of type %r!' % (name, pn, po.datatype))
         for pn, po in self.propertyDict.items():