RFR: JDK-8290020 Deadlock in leakprofiler::emit_events during shutdown

[Ludvig Janiuk]

Add a boolean parameter to Jfr::on_vm_shutdown to differentiate the "called from java" case, and in that case to not call JfrEmergencyDump::on_vm_shutdown.

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

Commit messages:
 - whitespace
 - whitespace
 - Simplify test
 - Fix test
 - Update test
 - Adding an option to detect call from java

Changes: https://git.openjdk.org/jdk/pull/9465/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9465&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8290020
  Stats: 43 lines in 6 files changed: 9 ins; 10 del; 24 mod
  Patch: https://git.openjdk.org/jdk/pull/9465.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9465/head:pull/9465

PR: https://git.openjdk.org/jdk/pull/9465