[crac] RFR: Report checkpoint processing to jcmd [v4]

[Ilarion Nakonechnyy]

> pass output stream from diagnosticCommand.cpp through java code into os_linux.cpp::VM_crac::doit()

Ilarion Nakonechnyy has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains seven commits:

 - Merge remote-tracking branch 'upstream/crac' into crac
 - ws correction
 - Rework closing the jcmd socket.
   New approach, a bit complicated but proper -
   save an AttachOperation ( from jcmd )
   and call "complete()"  as attach operation function.
 - whitespaces
 - Properly pass return code to jcmd peer,
   and pass correctly buffered output
 - Check the opened socket, if it is UNIX socked from jcmd.
 - Implementation of reporting
   checkpoint command execution to JCMD.

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Changes: https://git.openjdk.org/crac/pull/10/files
 Webrev: https://webrevs.openjdk.org/?repo=crac&pr=10&range=03
  Stats: 301 lines in 11 files changed: 238 ins; 18 del; 45 mod
  Patch: https://git.openjdk.org/crac/pull/10.diff
  Fetch: git fetch https://git.openjdk.org/crac pull/10/head:pull/10

PR: https://git.openjdk.org/crac/pull/10