[Chapel Merge] Estimate time-to-completion in many-to-one test be

Branch: refs/heads/master
Revision: c450dd4
Author: gbtitus
Log Message:

Merge pull request #17676 from gbtitus/mto-completion-estimation

Estimate time-to-completion in many-to-one test better.

(Reviewed by @ronawho.)

Long ago I screwed up the algebra when estimating how much more work
we will need to do to run for the desired length of time in the
many-to-one microbenchmark. Fix that. Now it only checks the time
a few times. It used to do so hundreds of times.

Modified Files:
M test/performance/comm/low-level/many-to-one.chpl

Compare: https://github.com/chapel-lang/chapel/compare/d3a8bd2bc030...c450dd45b1ac