lib/plugins/aws/rollback/index.js/AwsRollback/constructor
class AwsRollback:  constructor(serverless, options) {
    this.serverless = serverless;
    this.options = options;
    this.provider = this.serverless.getProvider('aws');

    Object.assign(
      this,
      validate,
      setBucketName,
      updateStack,
      monitorStack
    );

    this.hooks = {
      'before:rollback:initialize': () => BbPromise.bind(this)
        .then(this.validate),
      'rollback:rollback': () => BbPromise.bind(this)
        .then(this.setBucketName)
        .then(this.setStackToUpdate)
        .then(this.updateStack),
    };
  }