Not able to set on_failure_callback in default args

[madhavdube]

I am trying to set the default args as
default_args={'on_failure_callback': 'foo_function_str`}

the yaml config I am trying

dag_1:
   default_args:
       start_date: '1999-01-01'
       on_failure_callback: 'dags.utils.failures.send_alert' -- str representation of function
   

The other config I tried using on_failure_callback_file but this does not set the property in the default dict.

dag factory version - 0.8.0