Make get_dn parameter list more generic. Fix Attribute name regex.

The old name regex made it impossible to have Attribute instances with
names composed of more than two words separated by underscores.

ipalib/frontend.py

@@ -795,9 +795,9 @@ class Object(HasParam):
                 continue
             yield param
 
-    def get_dn(self, primary_key):
+    def get_dn(self, *args, **kwargs):
         """
-        Construct an LDAP DN from a primary_key.
+        Construct an LDAP DN.
         """
         raise NotImplementedError('%s.get_dn()' % self.name)
 
@@ -878,7 +878,7 @@ class Attribute(Plugin):
 
     def __init__(self):
         m = re.match(
-            '^([a-z][a-z0-9]+)_([a-z][a-z0-9]+)$',
+            '^([a-z][a-z0-9]+)_([a-z][a-z0-9]+(?:_[a-z][a-z0-9]+)*)$',
             self.__class__.__name__
         )
         assert m