TriggerDagRunOperator only works with the `raw` argument.

[paul-english]

I'm not too sure on the details about this, but trying to trigger a TriggerDagRunOperator usually fails with the following output.

> airflow run test_dag run_other_dag 2015-11-24
Sending to executor.
Traceback (most recent call last):
  File "/Users/penglish/.virtualenvs/athena/bin/airflow", line 6, in <module>
    exec(compile(open(__file__).read(), __file__, 'exec'))
  File "/Users/penglish/src/github.com/airbnb/airflow/airflow/bin/airflow", line 17, in <module>
    args.func(args)
  File "/Users/penglish/src/github.com/airbnb/airflow/airflow/bin/cli.py", line 145, in run
    raise AirflowException(msg)
airflow.utils.AirflowException: DAG [xxxxxxxxxx] could not be found

I think the issue is that the dagbag in the cli only includes the test_dag in it's list of dags. I noticed that there was a branch that directly runs the task instance if raw is set, and this seems to work.

This doesn't seem like desired behavior since trying to run a task from the web interface doesn't send the raw argument.

[t1m0thy]

Hi, I have a small fix in this patch that I believe fixes this bug.
https://github.com/t1m0thy/airflow/tree/patch-1

Once I get a chance to test it in the next couple of days and be sure it doesn't create any new bugs, I'll do a pull request.