Block build requests until environment builder is ready (#437)

* Add readiness probe
* Remove builder manager http api interface since we don’t use/need it
* Check environment builder status and block build requests until builder is ready
* Replace deprecated api extension interface
* Add healthy check to python env

environments/python/server.py

@@ -61,6 +61,10 @@ def loadv2():
 
     return ""
 
+@app.route('/healthz', methods=['GET'])
+def healthz():
+    return "", 200
+
 @app.route('/', methods=['GET', 'POST', 'PUT', 'HEAD', 'OPTIONS', 'DELETE'])
 def f():
     if userfunc == None: