swarming: Add server-side implementation for supplemental bot_config

appengine/swarming/test_env_handlers.py

Index: appengine/swarming/test_env_handlers.py
diff --git a/appengine/swarming/test_env_handlers.py b/appengine/swarming/test_env_handlers.py
index ebbabdacb1175d3753a329b0a6eef7dce8dff346..cab5a5a2794b4a8109b3d0d64910ebc3e5429a95 100644
--- a/appengine/swarming/test_env_handlers.py
+++ b/appengine/swarming/test_env_handlers.py
@@ -141,7 +141,7 @@ class AppTestBase(test_case.TestCase):
 
   # Bot
 
-  def do_handshake(self, bot='bot1'):
+  def do_handshake(self, bot='bot1', status=200):
     """Performs bot handshake, returns data to be sent to bot handlers.
 
     Also populates self.bot_version.
@@ -161,10 +161,16 @@ class AppTestBase(test_case.TestCase):
     }
     response = self.app.post_json(
         '/swarming/api/v1/bot/handshake',
-        params=params).json
+        params=params, status=status)
+    if status != 200:
+      return
+    response = response.json
     self.bot_version = response['bot_version']
     params['version'] = self.bot_version
     params['state']['bot_group_cfg_version'] = response['bot_group_cfg_version']
+    # A bit hackish but fine for unit testing purpose.
+    if response.get('bot_config'):
+      params['bot_config'] = response['bot_config']
     return params
 
   def bot_poll(self, bot='bot1'):