Set the batch size to improve throughput

Processing messages with a larger batch size (increased from the default of
100 to 1000 for telemetry and 2000 for FHR) has a large positive effect on
throughput.  More than a 2x speedup for Telemetry and maybe 3-5x speedup for
FHR.

Increasing Telemetry batch size from 1000 to 2000 didn't cause a significant
improvement in tests today (July 11, 2013).
Merge pull request #23 from mozilla-metrics/consumer-batch-size

Set the batch size to improve throughput