when validation_step/end not defined, val_loss still gets logged
Describe the bug
If the validation_step/end is not implemented by user, lightning still shows a mysterious validation loss in tqdm. Where does this come from?
To Reproduce
Steps to reproduce the behavior:

Take MNIST example in "basic_examples" folder (current master branch)
Uncomment validation_step and validation_end and run the gpu_template
Wait until epoch 2 starts
You will see:
Epoch 2:  14%|█▎        | 150/1095 [00:10<01:05, 14.35batch/s, batch_nb=149, gpu=0, loss=0.177, train_loss=0.261, v_nb=1, val_acc=0.939, val_loss=0.19]

Expected behavior
val_acc and val_loss should not be there. Where do these numbers come from?
Screenshots
If applicable, add screenshots to help explain your problem.
Desktop (please complete the following information):

OS: Ubuntu 18.04
Version: 0.5.3.2 (via pip install)