align dropout api name with pytorch

[BBuf]

align dropout api name with pytorch, is_training->training!!

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Speed stats:

GPU Name: GeForce GTX 1080 

OneFlow resnet50 time: 128.6ms (= 6427.8ms / 50, input_shape=[16, 3, 224, 224])
PyTorch resnet50 time: 141.3ms (= 7063.7ms / 50, input_shape=[16, 3, 224, 224])
Relative speed: 1.10 (= 141.3ms / 128.6ms)

OneFlow resnet50 time: 74.6ms (= 3731.4ms / 50, input_shape=[8, 3, 224, 224])
PyTorch resnet50 time: 86.2ms (= 4311.7ms / 50, input_shape=[8, 3, 224, 224])
Relative speed: 1.16 (= 86.2ms / 74.6ms)

OneFlow resnet50 time: 48.4ms (= 2421.2ms / 50, input_shape=[4, 3, 224, 224])
PyTorch resnet50 time: 57.5ms (= 2873.2ms / 50, input_shape=[4, 3, 224, 224])
Relative speed: 1.19 (= 57.5ms / 48.4ms)

OneFlow resnet50 time: 40.1ms (= 2005.8ms / 50, input_shape=[2, 3, 224, 224])
PyTorch resnet50 time: 47.3ms (= 2363.1ms / 50, input_shape=[2, 3, 224, 224])
Relative speed: 1.18 (= 47.3ms / 40.1ms)

OneFlow resnet50 time: 37.8ms (= 1891.3ms / 50, input_shape=[1, 3, 224, 224])
PyTorch resnet50 time: 42.5ms (= 2126.5ms / 50, input_shape=[1, 3, 224, 224])
Relative speed: 1.12 (= 42.5ms / 37.8ms)

OneFlow resnet50 time: 157.1ms (= 7856.1ms / 50, input_shape=[16, 3, 224, 224], ddp, world size=2)
PyTorch resnet50 time: 165.7ms (= 8283.0ms / 50, input_shape=[16, 3, 224, 224], ddp, world size=2)
Relative speed: 1.05 (= 165.7ms / 157.1ms)

OneFlow resnet50 time: 100.7ms (= 5037.2ms / 50, input_shape=[8, 3, 224, 224], ddp, world size=2)
PyTorch resnet50 time: 113.1ms (= 5654.2ms / 50, input_shape=[8, 3, 224, 224], ddp, world size=2)
Relative speed: 1.12 (= 113.1ms / 100.7ms)

OneFlow resnet50 time: 76.1ms (= 3806.5ms / 50, input_shape=[4, 3, 224, 224], ddp, world size=2)
PyTorch resnet50 time: 75.4ms (= 3771.1ms / 50, input_shape=[4, 3, 224, 224], ddp, world size=2)
Relative speed: 0.99 (= 75.4ms / 76.1ms)

OneFlow resnet50 time: 73.1ms (= 3656.5ms / 50, input_shape=[2, 3, 224, 224], ddp, world size=2)
PyTorch resnet50 time: 65.6ms (= 3278.4ms / 50, input_shape=[2, 3, 224, 224], ddp, world size=2)
Relative speed: 0.90 (= 65.6ms / 73.1ms)

OneFlow resnet50 time: 70.2ms (= 3511.5ms / 50, input_shape=[1, 3, 224, 224], ddp, world size=2)
PyTorch resnet50 time: 59.1ms (= 2957.1ms / 50, input_shape=[1, 3, 224, 224], ddp, world size=2)
Relative speed: 0.84 (= 59.1ms / 70.2ms)