RFR: 6554: Support JFR in OpenJDK 8

[Marcus Hirt]

This is for OpenJDK 8 implementations that have backported JFR, e.g. Azul's JDK. There is also a backport effort for OpenJDK 8 in general.

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

Commits:
 - b8a6680e: Spotless
 - c0d3e450: 6554: Support JFR in OpenJDK 8

Changes: https://git.openjdk.java.net/jmc/pull/19/files
 Webrev: https://webrevs.openjdk.java.net/jmc/19/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JMC-6554
  Stats: 176 lines in 10 files changed: 102 ins; 53 del; 21 mod
  Patch: https://git.openjdk.java.net/jmc/pull/19.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/19/head:pull/19

PR: https://git.openjdk.java.net/jmc/pull/19