Drop postgres database.

def drop_database(self):
        """ Drop postgres database. """
        self.print_message("Dropping database '%s'" % self.databases['destination']['name'])
        self.export_pgpassword('destination')
        args = [
            "dropdb",
            "--if-exists",
            self.databases['destination']['name'],
        ]
        args.extend(self.databases['destination']['args'])
        subprocess.check_call(args)