Add routine to trim output from tests in sub_test
Add routine to trim output from tests in sub_test

We were previously trimming output from tests in computePerfStats, but
that didn't handle all cases (timeout, ...). This change should prevent
us from making 400MB+ log files.

hildeth/chapel,chizarlicious/chapel,hildeth/chapel,chizarlicious/chapel,CoryMcCartan/chapel,CoryMcCartan/chapel,chizarlicious/chapel,chizarlicious/chapel,hildeth/chapel,chizarlicious/chapel,CoryMcCartan/chapel,chizarlicious/chapel,hildeth/chapel,CoryMcCartan/chapel,hildeth/chapel,CoryMcCartan/chapel,hildeth/chapel,CoryMcCartan/chapel,CoryMcCartan/chapel,chizarlicious/chapel,hildeth/chapel