fix intermittent test failures from race cond
Rename Metric.Type to Metric.DataType and rename StatType to RollupType
Drop STATSD_ prefix from rollup types
Merge pull request #189 from lakshmi-kannan/bf_types_refactor

RFR: (Refactor) Rename Metric.Type to Metric.DataType and rename StatType to RollupType
Merge pull request #188 from fourk/fix_intermittent_test_failures

Fix intermittent test failures from race condition