Function evaluate

Run evaluation. Run evaluation on dataset which is generated from a generator. Support evaluation on single GPU and multiple GPUs. Single GPU: 1. Run evaluation on the whole dataset (the generator generates the completed whole dataset). 2. Disply evaluation result. Multiple GP

(task,
             model,
             generator,
             args,
             dev_count,
             gpu_id,
             training_step,
             tag=None)