remote training service: mnist-keras example download data failed

[chicm-ms]

when multiple trial jobs on same machine, the downloading can be failed:

2020-03-21T16:02:00.2296265Z Downloading data from https://s3.amazonaws.com/img-datasets/mnist.npz
2020-03-21T16:02:00.2297049Z 
2020-03-21T16:02:00.2298385Z     8192/11490434 [..............................] - ETA: 0s
2020-03-21T16:02:00.2300214Z  3088384/11490434 [=======>......................] - ETA: 0s
2020-03-21T16:02:00.2301403Z 10387456/11490434 [==========================>...] - ETA: 0s
2020-03-21T16:02:00.2302636Z 11493376/11490434 [==============================] - 0s 0us/step
2020-03-21T16:02:00.2303356Z Using TensorFlow backend.
2020-03-21T16:02:00.2303910Z Bad magic number for file header
2020-03-21T16:02:00.2304485Z Traceback (most recent call last):
2020-03-21T16:02:00.2305442Z   File "mnist-keras.py", line 128, in <module>
2020-03-21T16:02:00.2306870Z     train(ARGS, PARAMS)
2020-03-21T16:02:00.2308104Z   File "mnist-keras.py", line 93, in train
2020-03-21T16:02:00.2309169Z     x_train, y_train, x_test, y_test = load_mnist_data(args)
2020-03-21T16:02:00.2310368Z   File "mnist-keras.py", line 66, in load_mnist_data
2020-03-21T16:02:00.2311171Z     (x_train, y_train), (x_test, y_test) = mnist.load_data()
2020-03-21T16:02:00.2312896Z   File "/usr/local/lib/python3.5/dist-packages/keras/datasets/mnist.py", line 25, in load_data
2020-03-21T16:02:00.2314205Z     x_train, y_train = f['x_train'], f['y_train']
2020-03-21T16:02:00.2315858Z   File "/usr/local/lib/python3.5/dist-packages/numpy/lib/npyio.py", line 228, in __getitem__
2020-03-21T16:02:00.2316586Z     bytes = self.zip.open(key)
2020-03-21T16:02:00.2317230Z   File "/usr/lib/python3.5/zipfile.py", line 1266, in open
2020-03-21T16:02:00.2317717Z     raise BadZipFile("Bad magic number for file header")
2020-03-21T16:02:00.2318262Z zipfile.BadZipFile: Bad magic number for file header
2020-03-21T16:02:00.2318708Z Traceback (most recent call last):
2020-03-21T16:02:00.2319995Z   File "mnist-keras.py", line 128, in <module>
2020-03-21T16:02:00.2320377Z     train(ARGS, PARAMS)
2020-03-21T16:02:00.2320906Z   File "mnist-keras.py", line 93, in train
2020-03-21T16:02:00.2321320Z     x_train, y_train, x_test, y_test = load_mnist_data(args)
2020-03-21T16:02:00.2321899Z   File "mnist-keras.py", line 66, in load_mnist_data
2020-03-21T16:02:00.2322372Z     (x_train, y_train), (x_test, y_test) = mnist.load_data()
2020-03-21T16:02:00.2323670Z   File "/usr/local/lib/python3.5/dist-packages/keras/datasets/mnist.py", line 25, in load_data
2020-03-21T16:02:00.2324931Z     x_train, y_train = f['x_train'], f['y_train']
2020-03-21T16:02:00.2326812Z   File "/usr/local/lib/python3.5/dist-packages/numpy/lib/npyio.py", line 228, in __getitem__
2020-03-21T16:02:00.2328780Z     bytes = self.zip.open(key)
2020-03-21T16:02:00.2330012Z   File "/usr/lib/python3.5/zipfile.py", line 1266, in open
2020-03-21T16:02:00.2331793Z     raise BadZipFile("Bad magic number for file header")
2020-03-21T16:02:00.2333246Z zipfile.BadZipFile: Bad magic number for file header
2020-03-21T16:02:00.2335105Z [2020-03-21 16:01:51.138132] INFO subprocess terminated. Exit code is 1. Quit
2020-03-21T16:02:00.2338708Z [2020-03-21 16:01:51.152957] INFO NNI trial keeper exit with code 1

[chicm-ms]

Fixed.