RFR 9: 8143016 : java/time/test/java/time/TestClock_System.java failed intermittently

[Roger Riggs]

Please review a test improvement to address an intermittent test failure in
the java.time System Clock test for microsecond support.

webrev:
   http://cr.openjdk.java.net/~rriggs/webrev-micros-8143016/

Issue:
   https://bugs.openjdk.java.net/browse/JDK-8143016

Thanks, Roger