fix inheritance problem with mixin

- a mixin should not inherit from module then it has Parameters
- Parameters in mixins must be complete, not just overrides
- check precedence of read_<param> or handler

Change-Id: I72d9355a1982770d1a99d9552a20330103c97edb

secop/server.py

@@ -228,11 +228,15 @@ class Server:
             errors.append(self.unknown_options(cls, opts))
         self.modules = OrderedDict()
         badclass = None
+        failed = set()  # python modules failed to load
         self.lastError = None
         for modname, options in self.module_cfg.items():
             opts = dict(options)
             try:
                 classname = opts.pop('class')
+                pymodule = classname.rpartition('.')[0]
+                if pymodule in failed:
+                    continue
                 cls = get_class(classname)
                 modobj = cls(modname, self.log.getChild(modname), opts, self)
                 # all used args should be popped from opts!
@@ -242,8 +246,12 @@ class Server:
             except ConfigError as e:
                 errors.append(str(e))
             except Exception as e:
-                badclass = classname
-                errors.append('error while loading %s' % badclass)
+                if str(e) == 'no such class':
+                    errors.append('%s not found' % classname)
+                else:
+                    failed.add(pymodule)
+                    badclass = classname
+                    errors.append('error importing %s' % pymodule)
 
         poll_table = dict()
         # all objs created, now start them up and interconnect