RFR: 8257234 : Add gz option to SA jmap to write a gzipped heap dump [v14]

[Lin Zang]

> 8257234 : Add gz option to SA jmap to write a gzipped heap dump

Lin Zang has updated the pull request incrementally with two additional commits since the last revision:

 - fix an issue of double printing error message.
 - fix jcmd jmap issue and add test in BascJMapTest and code refine

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1712/files
  - new: https://git.openjdk.java.net/jdk/pull/1712/files/db38b6a8..0d30aaf3

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1712&range=13
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1712&range=12-13

  Stats: 50 lines in 4 files changed: 27 ins; 7 del; 16 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1712.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1712/head:pull/1712

PR: https://git.openjdk.java.net/jdk/pull/1712