Update usgs pandas

- Re-factored loop to use `parse_metadata` and pandas `read_csv`
- Applied pep8 and pyflakes rules
-Reduced `conda-requirements.txt` and `pip-requirements.txt` to minimal depencies

@birdage Take a look if I broke anything.  If you think this is OK merge and update https://github.com/ioos/system-test/pull/177 so we can marge it at ioos/system