Benchmark-cli read command should support --format option (format conversion feature).

[cheqianh]

Currently ion-python-benchmark-cli read mode doesn't support --format option.

For example, given a binary ion file. Command python-benchmar-cli read --format ion_text will returns the benchmark time used for text format, and the --format options is ignored. In other words, the format will be decided by given file.

The format option should be enabled for read command, since the CLI may add more formats such as JSON in the future.

[cheqianh]

READ supports format option now, but requires a format conversion tool to enable arbitrary conversion.