Make TAU processor threadpool size configurable

The default type and unit processor threadpool size of 10 was causing a
massive bottleneck during ingestion. It would hold up the rest of the
ingestion pipeline during initial load of the metadata cache and when
persisting large loads of new entries in the metrics_metadata CF, as it
does the writes one at a time.
Set the TAU processor core pool size too
Merge pull request #298 from dlobue/configure_type_and_unit_processor_threadpool_size

Make TAU processor threadpool size configurable
Ignore metrics with 'null' metric values
Add test case for JSONContainer.toMetrics() with a null valued metric
Merge pull request #313 from lakshmi-kannan/bf_fix_null_metric_values

Ignore null valued metrics
Catch exception around converting JSONMetricContainer to metric objects conversion
Improve exception for metric type detection
Add test case for handling BigInteger
Merge pull request #314 from lakshmi-kannan/bf_big_integer_no_http_response

Big integers as metric values invoke no HTTP response from BF.
Force cast BigInteger to Double if it's less than Double.MAX_VALUE
log when a bigint greater than Double.MAX_VALUE is encountered
Merge pull request #315 from lakshmi-kannan/bf_big_integer_no_http_response

Force cast BigInteger to Double if it's less than Double.MAX_VALUE