RFR: 8271949: dumppath in -XX:FlightRecorderOptions does not affect [v6]

[Yasumasa Suenaga]

> We set `dumppath` in `-XX:FlightRecorderOptions` or `JFR.configure dumppath` jcmd when we want to set emergency dump path. However they do not afffect.
> 
> ### -XX:FlightRecorderOptions
> 
> 
> $ java -XX:FlightRecorderOptions=dumppath=`pwd` -XX:StartFlightRecording -Xlog:exceptions=info --version
> [0.032s][info][exceptions] Exception <a 'java/lang/IllegalArgumentException'{0x00000007470163b8}: Unknown argument 'dumppath' in diagnostic command.> (0x00000007470163b8)
> thrown [open/src/hotspot/share/services/diagnosticFramework.cpp, line 215]
> for thread 0x00007f4f700236a0
> [0.033s][error][arguments ] Unknown argument 'dumppath' in diagnostic command.
> Error occurred during initialization of VM
> Failure when starting JFR on_create_vm_2
> 
> 
> ### jcmd
> 
> `jcmd` shows the configuration change was succeeded, but it would not affect.
> 
> 
> $ jcmd 1046 JFR.configure dumppath=/tmp
> 1046:
> Dump path: /tmp

Yasumasa Suenaga has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 10 additional commits since the last revision:

 - Use current directory if emergency dump fails on specified path
 - Merge remote-tracking branch 'upstream/master' into JDK-8271949
 - Print warning message instead of throwing exception if JFR will not write emergency dump
 - Merge remote-tracking branch 'upstream/master' into JDK-8271949
 - Set absolute path to JFR emergency dump path
 - Check write permission on JFR emergency dump path in configuration
 - Update testcase
 - Merge remote-tracking branch 'upstream/master' into JDK-8271949
 - Remove USER_HOME
 - 8271949: dumppath in -XX:FlightRecorderOptions does not affect

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5019/files
  - new: https://git.openjdk.java.net/jdk/pull/5019/files/b8da8def..d4a7674d

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5019&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5019&range=04-05

  Stats: 43314 lines in 1367 files changed: 28430 ins; 8430 del; 6454 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5019.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5019/head:pull/5019

PR: https://git.openjdk.java.net/jdk/pull/5019