Handle stack create/update rollbacks as failures

@@ -25,6 +25,7 @@ LOG = logging.getLogger(__name__)
 class Kappa(object):
 
     completed_states = ('CREATE_COMPLETE', 'UPDATE_COMPLETE')
+    failed_states = ('ROLLBACK_COMPLETE')
 
     def __init__(self, config):
         self.config = config
@@ -67,6 +68,8 @@ class Kappa(object):
             LOG.debug('Stack status is: %s', status)
             if status in self.completed_states:
                 done = True
+            if status in self.failed_states:
+                raise ValueError('Could not create stack %s: %s' % (stack_name, status))
 
     def get_role_arn(self, role_name):
         role_arn = None