benchmark: allow no duration in benchmark tests

Imprecision in process.hrtime() in some situations can result in a zero
duration being used as a denominator in benchmark tests. This would
almost certainly never happen in real benchmarks. It is only likely in
very short benchmarks like the type we run in our test suite to just
make sure that the benchmark code is runnable.

So, if the environment variable that we use in tests to indicate "allow
ludicrously short benchmarks" is set, convert a zero duration for
a benchmark to 1 nano-second.

PR-URL: https://github.com/nodejs/node/pull/13110
Fixes: https://github.com/nodejs/node/issues/13102
Fixes: https://github.com/nodejs/node/issues/12433


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>