Don't escape servername in json blobs

jupyterhub/proxy.py

@@ -288,7 +288,7 @@ class Proxy(LoggingConfigurable):
         await self.add_route(
             spawner.proxy_spec,
             spawner.server.host,
-            {'user': user.name, 'server_name': url_escape_path(server_name)},
+            {'user': user.name, 'server_name': server_name},
         )
 
     async def delete_user(self, user, server_name=''):

jupyterhub/tests/test_named_servers.py

@@ -175,7 +175,7 @@ async def test_create_invalid_named_server(app, named_servers):
         r.raise_for_status()
     assert exc.value.response.json() == {
         'status': 400,
-        'message': 'Invalid server_name: a$/b',
+        'message': "Invalid server_name (may not contain '/'): a$/b",
     }