Binary API CLI Test: Removed redundant class and fixed -k parameter.

Previously, the parameters from argparse were passed into an empty
class, which was unneccessary. That class has been removed and the
calling code simplified.

The action='store_const' wasn't appropriate for -k, --key, whereas
if you passed a parameter for -k, the script wouldn't recognize it.
Now, the action is the default and const=None has been replaced by
a more suitable default=None. The code now accepts -k passed from
the command line.