Add options to command line.

def options(self, parser, env):
        """
        Add options to command line.
        """
        Plugin.options(self, parser, env)
        parser.add_option('--xcoverage-file', action='store',
                          default=env.get('NOSE_XCOVER_FILE', 'coverage.xml'),
                          dest='xcoverage_file',
                          metavar="FILE",
                          help='Path to xml coverage report.'
                          'Default is coverage.xml in the working directory. '
                          '[NOSE_XCOVERAGE_FILE]')
        parser.add_option('--xcoverage-to-stdout', action='store',
                          default=env.get('NOSE_XCOVER_TO_STDOUT', True),
                          dest='xcoverage_to_stdout',
                          help='Print coverage information to stdout.'
                          'Default is True (output coverage information to stdout). '
                          '[NOSE_XCOVER_TO_STDOUT]')