Performance issues in the program

[DLPerf]

Hello,I found a performance issue in the definition of create_ground_truth_file ,
lmb-freiburg/demon/blob/master/examples/evaluation.py,
session = tf.InteractiveSession was repeatedly called and was not closed.
I think it will increase the efficiency and avoid out of memory if you close this session after using it.

The same issues also exist in session = tf.InteractiveSession

Here are two files to support this issue,support1 and support2

Looking forward to your reply. Btw, I am very glad to create a PR to fix it if you are too busy.

[benjaminum]

Sure, please create a PR.