RFR: 8286706: JFR: 'jfr scrub' should overwrite output

[Erik Gahlin]

Could I have a review of a change that makes the 'jfr scrub' overwrite the output file if it already exists.

Testing: /test/jdk/jdk/jfr/tool  (Mac, Linux, Windows)

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.java.net/jdk/pull/8728/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8728&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286706
  Stats: 35 lines in 2 files changed: 34 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8728.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8728/head:pull/8728

PR: https://git.openjdk.java.net/jdk/pull/8728