map_labels fails for n_classes > 1

[hvgazula]

    File "/net/vast-storage/scratch/vast/gablab/hgazula/nobrainer/nobrainer/dataset.py", line 338, in None  *
        lambda x, y: (x, tf.one_hot(y, self.n_classes))

    TypeError: Value passed to parameter 'indices' has DataType float32 not in list of allowed values: uint8, int8, int32, int64

Solution: cast y into one of the int types and the rest should flow.

TODO: check the same with n_classes = 2

[hvgazula]

tf.cast is the way to go but it will render the casting in binarize redundant. Need to clean this up a bit.