Potentially change the jarvis hostfile format to support node allocation + grouping

[lukemartinlogan]

Right now the jarvis hostfile is just a bag of hosts. Users will probably know high-level properties about the nodes they are going to allocate. Like "I want 10 compute nodes" and "15 storage nodes". However, right now, we require users to know the exact hostnames before-hand, which is not typically realistic. It is in Ares, but not anywhere else. We need to augment the jarvis hostfile to be either a high-level job submission or a detailed node list.