state: use blocking queries to mirror critical Nomad state internally

[jrasell]

The number of ad-hoc Nomad API queries in a medium/large Nomad cluster would put a significant amount of pressure on the Nomad API. Thankfully Nomad supports blocking queries to reduce this load pressure. The Autoscaler should therefore use blocking queries on key API integrations, and process data to store internally for fast lookups. This data would all be ephemeral; the Autoscaler can populate all its data upon startup.