Allow specifying user when creating a group using the factory

With this, we're able to create a group owned by a specific user.

ckan/new_tests/factories.py

@@ -117,6 +117,8 @@ class Group(factory.Factory):
     # Generate a different group name param for each user that gets created.
     name = factory.Sequence(lambda n: 'test_group_{n}'.format(n=n))
 
+    user = factory.LazyAttribute(lambda _: helpers.call_action('get_site_user'))
+
     @classmethod
     def _build(cls, target_class, *args, **kwargs):
         raise NotImplementedError(".build() isn't supported in CKAN")
@@ -126,11 +128,10 @@ def _create(cls, target_class, *args, **kwargs):
         if args:
             assert False, "Positional args aren't supported, use keyword args."
 
-        #TODO: we will need to be able to define this when creating the
-        #      instance perhaps passing a 'user' param?
         context = {
-            'user': helpers.call_action('get_site_user')['name']
+            'user': kwargs['user']['name']
         }
+        del kwargs['user']
 
         group_dict = helpers.call_action('group_create',
                                          context=context,