Add support for running some jobs on CPUs

[lewfish]

When using Batch, we would like to be able to run some jobs on the CPU and some on GPU. To do this, we will need to modify the RV profile configuration to specify CPU and GPU resources. Currently a config looks like:

[AWS_BATCH]
job_queue=raster-vision-lewfish-p3
job_definition=raster-vision-lewfish-p3

but it should become something like

[AWS_BATCH]
cpu_job_queue=raster-vision-lewfish-m4
cpu_job_definition=raster-vision-lewfish-m4
gpu_job_queue=raster-vision-lewfish-p3
gpu_job_definition=raster-vision-lewfish-p3

Then the aws_batch runner needs to be modified so that it picks the correct job queue and job def for the command. Each command needs to have a mechanism for deciding which queue should be used (analyze, chip, and eval seem like good candidates for CPU). When jobs are submitted, the required number of CPU cores needs to be specified. It should stay at the current value for GPUs, but CPU jobs should only require one core.

A prerequisite for this issue is #634