Fix bug in repr of davstorage

tests/storage/__init__.py

@@ -178,3 +178,7 @@ class StorageTests(object):
             (href, etag) for href, item, etag
             in s.get_multi(href for href, etag in iteritems(info))
         ) == info
+
+    def test_repr(self):
+        s = self._get_storage()
+        assert self.storage_class.__name__ in repr(s)

vdirsyncer/storage/dav.py

@@ -264,6 +264,10 @@ class DavStorage(Storage):
                                   useragent, dav_header=self.dav_header)
         self.collection = collection
 
+        # defined for _repr_attributes
+        self.username = username  
+        self.url = url
+
     @classmethod
     def discover(cls, url, **kwargs):
         if kwargs.pop('collection', None) is not None: