'Parse the CLI options
:returns: (cli_opts, cli_args)'

def parse_cli(self):

    parser = OptionParser(usage=self.usage, description=self.description)
    parser.add_option('-i', '--input', type='string', help=self.input_help)
    if self.has_output:
        parser.add_option('-o', '--output', type='string', help=self.output_help)
    parser.add_option('--keyform', help=('Key    format    of    the    %s    key    -    default    PEM' % self.keyname), choices=('PEM', 'DER'), default='PEM')
    (cli, cli_args) = parser.parse_args(sys.argv[1:])
    if (len(cli_args) != self.expected_cli_args):
        parser.print_help()
        raise SystemExit(1)
    return (cli, cli_args)
