title: "naive datetime is disallowed" when running Bash command using Apache Airflow
body: <p>It is looking like <code>sqlAlchemy</code> might have had a facelift since the time that the  <code>Airflow</code> tutorial were written:  it is not accepting a date in the format of <code>YYYY-DD-MM</code> that is shown in the tutorial at <a href="http://pythonhosted.org/airflow/tutorial.html" rel="nofollow noreferrer">http://pythonhosted.org/airflow/tutorial.html</a> : </p>
  
  <pre><code> $airflow test tutorial print_date  2017-12-30
  [2017-12-29 19:10:40,695] {__init__.py:45} INFO - Using executor SequentialExecutor
  [2017-12-29 19:10:40,745] {models.py:194} INFO - Filling up the DagBag from /git/airflow/home/dags
  Traceback (most recent call last):
    File "/usr/local/bin/airflow", line 4, in &lt;module&gt;
      __import__('pkg_resources').run_script('apache-airflow==1.10.0.dev0+incubating', 'airflow')
    File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 748, in run_script
      self.require(requires)[0].run_script(script_name, ns)
    ..
     File "build/bdist.macosx-10.12-x86_64/egg/sqlalchemy/engine/default.py", line 623, in _init_compiled
    File "build/bdist.macosx-10.12-x86_64/egg/sqlalchemy/sql/type_api.py", line 1074, in process
    File "build/bdist.macosx-10.12-x86_64/egg/sqlalchemy_utc.py", line 31, in process_bind_param
  sqlalchemy.exc.StatementError: (exceptions.ValueError) naive datetime is disallowed [SQL: u'SELECT task_instance.try_number AS task_instance_try_number, task_instance.task_id AS task_instance_task_id, task_instance.dag_id AS task_instance_dag_id, task_instance.execution_date AS task_instance_execution_date, task_instance.start_date AS task_instance_start_date, task_instance.end_date AS task_instance_end_date, task_instance.duration AS task_instance_duration, task_instance.state AS task_instance_state, task_instance.max_tries AS task_instance_max_tries, task_instance.hostname AS task_instance_hostname, task_instance.unixname AS task_instance_unixname, task_instance.job_id AS task_instance_job_id, task_instance.pool AS task_instance_pool, task_instance.queue AS task_instance_queue, task_instance.priority_weight AS task_instance_priority_weight, task_instance.operator AS task_instance_operator, task_instance.queued_dttm AS task_instance_queued_dttm, task_instance.pid AS task_instance_pid \nFROM task_instance \nWHERE task_instance.dag_id = ? AND task_instance.task_id = ? AND task_instance.execution_date = ?\n LIMIT ? OFFSET ?'] [parameters: [{}]]
  </code></pre>
  
  <p>What is the format <strong><em>now</em></strong> required by <code>sqlAlchemy</code> ?  (It appears to be a matter of a missing <code>timezone</code> - so I'm also looking into that ..)</p>