fio: report percentiles for slat, clat, lat

fio: report percentiles for slat, clat, lat

Currently, fio can report percentiles for either completion latencies or
total latencies. This patch adds the ability to simultaneously report
percentiles for submission, completion, and total latencies.

- simplify the JSON lat percentile reporting code
- parsing the JSON output will be unaffected, although now setting
lat_percentiles=1 no longer suppresses clat percentiles
- this may break parsing of the normal output since more latency
percentile blocks may be displayed
- to maintain backward compatibility in the terse output, total
latencies are reported if lat_percentiles=1 even when clat percentiles
have also been computed
- change the gtod_reduce callback to only change option values when
gtod_reduce=1
- for the new cmdprio_percentage latencies, if lat_percentiles=1,
*total* latency percentiles will be tracked. Otherwise, *completion*
latency percentiles will be tracked.
- also make sure we skip the high/low priority latency code if we are
producing output for sync latencies.
- make add_slat_sample use an unsigned long long for the time to be
consistent with other functions

Signed-off-by: Vincent Fu <vincent.fu@wdc.com>