Performance issue in the definition of main_unsupervised(P1)

[DLPerf]

Hello, I found a performance issue in the definition of main_unsupervised, code/ae/autoencoder.py, tf.reshape will be created repeatedly during program execution, resulting in reduced efficiency. I think it should be created before the loop.

The same issue exist in:

• tf.reshape(input_pl,... in line 430

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