error when the model has tf.cond

[flyree]

tf.cond is constructed with switch and merge operations.

There are two issues:

1. The current code do not support those two operations (I implement those operations on my own).
2. The fault injected graph seems not correct when there is tf.cond.

This link explains how tf.cond works.

https://towardsdatascience.com/tensorflow-control-flow-tf-cond-903e020e722a