Out of memory when restarting training process

[lewfish]

In theory, if you run train_ec2.sh and exit before training completes, and then restart the job, it should pick up where it left off. But this doesn't actually work because on the second run, TF emits an out of memory error. We should isolate the exact conditions when this occurs and file an issue in the repo for TF Object Detection. We should also check to see if there's an issue already there.

[lewfish]

This appears to be working locally now. We should check this on EC2.