Use ContainerStatsSample to store samples because CPU usages are
cumilative
unit tests for stats sample
create sample from a constructor
usge container stats sample
unit test for sampling
ignore sample if it leads cpu utilization < 0
unit test for NewSample()
change comments
remove avg memory usage
gofmt -r "ContainerStatsSummary->ContainerStatsPercentiles"
remove float opts.
Ignore the error because its' same as nil sample
correct a unit test
comment for intZipuint64
change var names
set timestamp by default. This behavior cannot be changed by users
use memory/cpu trace instead of random numbers
nil in a wrong place
percentile
put boilerplate into a function