test - Flesh out randread statistics reporting
* Cleanup the output. Report the aggregate IOPS, average latency,
aggregate bandwidth, low and high latencies, and the standard
deviation for the test on a per-second basis.
* Standard deviation notes:
68% Of the samples are within 1 standard deviation, so if the
reported stddev is 7uS, then 68% of the samples are +/- 7uS
of the average reported value.
95.45% Of the samples are within 2 standard deviations. +/- 14uS
in the example.
99.73% Of the samples are within 3 standard deviations. +/- 21uS
in the example.