Summary report no longer outputs summary of errors

[frankborden]

This change switched the reporter to use a buffered logger that gets passed in to reportTestFileResults(), but it stores the bufferedlogger and reuses it in onTestRunFinished() for further logging.

However TestRunnerCli is not aware of the re-use and flushes the buffered logs only after reportTestFileResults(), meaning the buffered logs added in onTestRunFinished() are never pushed to the stdout.

We observed this starting when we bumped @web/test-runner from 0.14.0 to 0.15.3

[poucet]

Any update on this? This is causing us to revert back to 0.14.0