RFR: 8267893: Improve jtreg test failure handler do get native/mixed stack traces for cores and live processes [v3]

[Leonid Mesnik]

> EFH is improved to process cores and get mixed stack traces with jhsdb and native stack traces with gdb/lldb. It might be useful because hs_err doesn't contain info about all threads, sometimes it is even not generated.

Leonid Mesnik has updated the pull request incrementally with one additional commit since the last revision:

  README updated.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4234/files
  - new: https://git.openjdk.java.net/jdk/pull/4234/files/cb1eb944..c48542b5

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4234&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4234&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4234.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4234/head:pull/4234

PR: https://git.openjdk.java.net/jdk/pull/4234