Split some big files into small ones for better reading

[GaryShen2008]

Problem:
Some files like nds_transocde.py, nds_bench.py are too big to read.

Expectation:
We should move out some parts in these big files to new files.
Like get_schemas in nds_transcode.py, we can create a new file to only define schema related, and it's also referred by multiple python scripts.
In nds_bench.py, we can move out the functions which analyze the report file to some utils file, so that only keep the step functions and main process, it should be clear to read.

[GaryShen2008]

It seems not easy to move the code of reading and writing report file to one place.
We can consider it in the future.