RFR: 8251843: jfr/tool/TestPrintJSON.java fails intermittently

[Erik Gahlin]

8251843: jfr/tool/TestPrintJSON.java fails intermittently

-------------

Commit messages:
 - Initial fix

Changes: https://git.openjdk.java.net/jdk/pull/1589/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1589&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8251843
  Stats: 31 lines in 1 file changed: 24 ins; 1 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1589.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1589/head:pull/1589

PR: https://git.openjdk.java.net/jdk/pull/1589