Zhiyuan He

### Motivation [OpenPAI protocol]() support users to specify `prerequisites` (e.g. `dockerimage`, `data`, and `script`) and then reference them in `taskrole`. There are some limitations in current version. - current solution...

Some PAI services, like the alert handler, and the incoming DB GCer, need to access rest-server. Thus, it always needs cluster admin to set a token manually for the service....