Processing a group of tasks.

def process(self, document):
        """Processing a group of tasks."""
        self.logger.info("Processing group of tasks (parallel=%s)", self.get_parallel_mode())
        self.pipeline.data.env_list[2] = {}

        output, shells = [], []
        result = Adapter({'success': True, 'output': []})
        for task_entry in document:
            key, entry = list(task_entry.items())[0]

            if (not self.parallel or key == 'env') and len(shells) > 0:
                result = Adapter(self.process_shells(shells))
                output += result.output
                shells = []
                if not result.success:
                    break

            if key == 'env':
                self.pipeline.data.env_list[2].update(entry)

            elif key in ['shell', 'docker(container)', 'docker(image)', 'python',
                         'packer', 'ansible(simple)']:
                self.prepare_shell_data(shells, key, entry)

        if result.success:
            result = Adapter(self.process_shells(shells))
            output += result.output

        self.event.delegate(result.success)
        return {'success': result.success, 'output': output}