Fix argument name that did not let users to sign up in runbot.

See https://github.com/OCA/server-tools/pull/277#discussion_r42502847

auth_from_http_remote_user/res_users.py

@@ -34,10 +34,10 @@ class res_users(orm.Model):
                                readonly=True),
     }
 
-    def copy(self, cr, uid, rid, defaults=None, context=None):
-        defaults = defaults or {}
-        defaults['sso_key'] = False
-        return super(res_users, self).copy(cr, uid, rid, defaults, context)
+    def copy(self, cr, uid, rid, default=None, context=None):
+        default = default or {}
+        default['sso_key'] = False
+        return super(res_users, self).copy(cr, uid, rid, default, context)
 
     def check_credentials(self, cr, uid, password):
         try: