grpc samples: specify type on --sample_rate to prevent TypeError

[zackse]

The --sample_rate argument in speech/grpc/transcribe.py and speech/grpc/transcribe_async.py did not specify a type, which meant the value would be treated as a string, resulting in an exception during protobuf conversion:

$ python transcribe.py --encoding FLAC --sample_rate 16000 gs://path/to/my.flac
Traceback (most recent call last):
  File "transcribe.py", line 95, in <module>
    main(args.input_uri, args.encoding, args.sample_rate)
  File "transcribe.py", line 66, in main
    language_code='en-US',  # a BCP-47 language tag
  File "/Users/zackse/code/python/contrib/python-docs-samples/speech/api-client/env/lib/python2.7/site-packages/google/protobuf/internal/python_message.py", line 535, in init
    _ReraiseTypeErrorWithFieldName(message_descriptor.name, field_name)
  File "/Users/zackse/code/python/contrib/python-docs-samples/speech/api-client/env/lib/python2.7/site-packages/google/protobuf/internal/python_message.py", line 455, in _ReraiseTypeErrorWithFieldName
    six.reraise(type(exc), exc, sys.exc_info()[2])
  File "/Users/zackse/code/python/contrib/python-docs-samples/speech/api-client/env/lib/python2.7/site-packages/google/protobuf/internal/python_message.py", line 533, in init
    setattr(self, field_name, field_value)
  File "/Users/zackse/code/python/contrib/python-docs-samples/speech/api-client/env/lib/python2.7/site-packages/google/protobuf/internal/python_message.py", line 669, in field_setter
    new_value = type_checker.CheckValue(new_value)
  File "/Users/zackse/code/python/contrib/python-docs-samples/speech/api-client/env/lib/python2.7/site-packages/google/protobuf/internal/type_checkers.py", line 132, in CheckValue
    raise TypeError(message)
TypeError: '16000' has type <type 'str'>, but expected one of: (<type 'int'>, <type 'long'>) for field RecognitionConfig.sample_rate

Hope this helps. Thanks for this service and the samples!

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[zackse]

I signed the CLA.

[googlebot]

CLAs look good, thanks!

[puneith]

@zackse LGTM. Thanks for your contribution!