test: change duration_ms to duration

The test script (tools/test.py) logs duration as "duration_ms: x.y".
This is confusing (as the duration is measured in seconds).

New example output: duration: 0.212s

PR-URL: #7133
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Claudio Rodriguez <cjrodr@yahoo.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

tools/test.py

@@ -310,7 +310,7 @@ def HasRun(self, output):
  (duration.seconds + duration.days * 24 * 3600) * 10**6) / 10**6
 
  logger.info(' ---')
- logger.info(' duration_ms: %d.%d' % (total_seconds, duration.microseconds / 1000))
+ logger.info(' duration: %d.%ds' % (total_seconds, duration.microseconds / 1000))
  logger.info(' ...')
 
  def Done(self):