Fix generate_text.sh Megatron text-generation example working w/ DS inference

[lekurile]

This PR gets text-generation working in the examples/generate_text.sh example working w/ DS inference enabled. For the main fix, the sample_sequence_batch function has been updated to perform the softmax when calculating log_probs, instead of setting it to 1's using torch.ones_like(...), although a few minor fixes were applied as well. Extra whitespace is also removed.

Currently, the examples/generate_text.sh example produces the same nonsensical output irrespective of input context or whether DS inference is enabled or not:

Oz jewelry Hod BombCook hiber csivalry Consumptionysics discipline wholesale aversionwic authoritativeduct...

This PR gets the example working w/o DS inference, e.g.:

Context: Hiking in nature is

Megatron-LM:  a far cry from schooldays, when a mountaineer would rely on...

In conjunction with PR #2579 in the DeepSpeed repo, the example also works w/ DS inference enabled e.g.:

Context: Hiking in nature is

Megatron-LM:  a far cry from schooldays, when a mountaineer would rely on...

Context: The engine of a car

Megatron-LM:  , after the oil is drained, oil is piped out of the engine...

[RezaYazdaniAminabadi]

All LGTM :)