Push up sys.exit to bin/aws

The clidriver class now only returns RCs, and
bin/aws actually calls sys.exit.
Remove unused imports in clidriver
Fix long line lengths
Refactor main parser to not store parser attribute

Instead it is passed around as needed.  This allowed
me to refactor the parsers to be more consistent with each other.
Now a 'create_*_parser' will return an ``argparse.ArgumentParser``
object, and all of the logic of chaining these parsers together
has been extracted out of the create_*_parser methods and into a
_parse_args method that is used by both ``test()`` and ``main()``.