title: Airflow custom operator variables
body: <p>I need to pass Airflow connection settings(AWS, Postgres) to docker container environment variables <br />
  I'm trying to do this using custom Operator and BaseHook. \</p>
  <pre><code>class S3ToPostgresDockerOperator(DockerOperator):
      @apply_defaults
      def __init__(self, aws_conn_id='aws_default', postgres_conn_id='postgres_default', **kwargs):
          super(S3ToPostgresDockerOperator, self).__init__(**kwargs)
          self.aws_conn = BaseHook.get_connection(aws_conn_id)
          self.pg_conn = BaseHook.get_connection(postgres_conn_id)
  </code></pre>
  <p>Is it possible to do something like that, or if not how should I do it?</p>
  <pre><code>    java_unpack_csv = S3ToPostgresDockerOperator(
          ...
          environment={
              'AWS_ACCESS_KEY': '{{ ??? }}',
              'AWS_SECRET_KEY': '{{ ??? }}'
          }
      )
  </code></pre>