CPU / GPU configuration to avoid resource contention

[ncollier]

Add functionality for setting number of threads per run / which GPU to use per run in order to avoid resource contention / starvation when running multiple runs on the same node.

Thread config for Keras + tensor flow:

keras-team/keras#4740
http://stackoverflow.com/questions/34389945/changing-the-number-of-threads-in-tensorflow-on-cifar10

W/r to GPU, the env var CUDA_VISIBLE_DEVICES can be used, but we'd need away to figure out which device was free.

http://stackoverflow.com/questions/37893755/tensorflow-set-cuda-visible-devices-within-jupyter