reset_default_graph()
Clears the default graph stack and resets the global default graph.
NOTE: The default graph is a property of the current thread. This
function applies only to the current thread. Calling this function while
a `tf.Session` or `tf.InteractiveSession` is active will result in undefined
behavior. Using any previously created `tf.Operation` or `tf.Tensor` objects
after calling this function will result in undefined behavior.
Raises:
AssertionError: If this function is called within a nested graph.
