Incorrect time left when resuming training

[friggog]

Not exactly a major issue, but

monodepth/monodepth_main.py

Line 168 in 5bc4bb1

training_time_left = (num_total_steps / step - 1.0) * time_sofar

Should be
training_time_left = ((num_total_steps - step) / (step - start_step)) * time_sofar