print slurm job ID when `renee cache` job is submitted

Good suggestion from @kcgfarb:

> add a slurm ID to the cache function output (much like the build and run functions produce the line `Successfully submitted master job: 55985237`

Currently it is easy for users to miss that `renee cache` actually submits a slurm job, and mistakenly believe it has completed when really it is still running.