Ingester/Submitter: Remove sleeps

[bartelink]

Improves the baseline impl of two key components in the Propulsion pipeline:

• Ingester: per Reader (Partition, Tranche etc) loop that manages:
  • accepting data from a single partition's Reader
  • managing the checkpointing as batches are confirmed complete
• Submitter: single loop that manages:
  • ingesting items supplied by the Ingester instances
  • propagating items into the Scheduler promptly and fairly

The key improvement is that the Pump methods now sleep until a trigger wakes them, rather than using a short sleep time and proactively checking whether some propagation activity has become possible. This provides the following benefits:

• there's no need to consider/tune the sleep interval
• under low load, there's dramatically less activity (CPU usage)
• under high load, there's never an overly long sleep (which might waste potential processing time for a downstream activity)

Also:

• Consolidated logging to have a single line of output
• de-emphasizing cycle counts and/or other information that was previously an input to troubleshooting and/or tuning sleep intervals etc
• Replaced defaulting of ingesterStatsInterval to 5 minutes with an explicit argument (which defaults to the statsInterval in some cases)