Add portList to PAI mode configurations

[ultmaster]

What would you like to be added: Add an optional field portList to configurations when using PAI mode.

Why is this needed: I want to use see my tensorboard on PAI. Currently I follow the practice below: launch a tensorboard in the script submitted to PAI in the background, then launch my training. However, I cannot access my tensorboard without a open port. PAI has provided an option, so that I can access the port using something like $PAI_PORT_LIST_main_0_tensorboard, but this option is not accessible from the interface that NNI has provided.

Without this feature, how does current nni work: Indeed we can find a workaround like downloading the event files and view it locally; but I can imagine adding this feature will provide great convenience for not only tensorboard, but also visdom and other web-dashboard-based tools.

Components that may involve changes: trainingServices logic, configuration settings.

Brief description of your proposal if any:

[ultmaster]

Merged