add more tests and fixes for command inheritance

- fix CommandType.__repr__
- secop/modules.py: command properties are allowed to be configured:
   - section 2: remove comment and rename
   - section 3: all accessible properties should be checked
- command description should be inherited also when taken from docstring
- move test for command inheritance to test_modules.py
- added tests to check for valid properties of commands

Change-Id: I5fd04e03be1faec5e54fed9735620bc5dc0f89c0

secop/datatypes.py

@@ -955,10 +955,9 @@ class CommandType(DataType):
         return props
 
     def __repr__(self):
-        argstr = repr(self.argument) if self.argument else ''
         if self.result is None:
-            return 'CommandType(%s)' % argstr
-        return 'CommandType(%s, %s)' % (argstr, repr(self.result))
+            return 'CommandType(%s)' % (repr(self.argument) if self.argument else '')
+        return 'CommandType(%s, %s)' % (repr(self.argument), repr(self.result))
 
     def __call__(self, value):
         """return the validated argument value or raise"""