Major rework to merge most of the changes from the NCCL internal
tests into the public ones
Added "-m <agg_iters>" operation aggregation option.
Data integrity checking is now much more performant at scale.
Startup times at scale are improved.
Test latency units are now displayed in usec.
Wenkai Du
Gilbert Lee
Stanley Tsang
David Addison
Sylvain Jeaugey