No error checking if incorrect image_id specified in clouds.conf

[tvoran]

$ ./automaton.py -l
2013-09-19 15:21:52,009 - __main__         - INFO     - Starting Automaton
Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/local/Cellar/python/2.7.5/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py", line 808, in __bootstrap_inner
    self.run()
  File "./automaton.py", line 48, in run
    cluster.launch()
  File "/Users/voran/projects/git/automaton/resources/cluster/clusters.py", line 75, in launch
    reservation = self.clouds[i].boot_image()
  File "/Users/voran/projects/git/automaton/resources/cloud/clouds.py", line 79, in boot_image
    boot_result = image_object.run(key_name=self.config.globals.key_name,
AttributeError: 'NoneType' object has no attribute 'run'