RFR: 8257234 : Add gz option to SA jmap to write a gzipped heap dump [v3]

[Lin Zang]

On Fri, 8 Jan 2021 13:21:21 GMT, Lin Zang <lzang at openjdk.org> wrote:

>> Changes requested by cjplummer (Reviewer).
>
> Hi @plummercj ,
> Thanks very much for reviewing!
> Sorry that I got stuck on other work and didn't read review message timely. 
> I will go through your suggestions carefully and  try to fix all issues you mentioned ASAP. 
> Thanks and Happy New Year!
> -Lin

This PR has passed tier1 on my linux x86_64 box.
seems the fail of pre-submit test is cause by environment issue.

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