RFR: CODETOOLS-7903325: jtreg check for macos version should take into account the process exit code

[Iris Clark]

On Thu, 22 Sep 2022 17:13:26 GMT, Jonathan Gibbons <jjg at openjdk.org> wrote:

> Please review a simple change to improve the reporting in the check for the macOS version.
> 
> Tested by temporarily modifying the code in place to change the command or its exit code.

Marked as reviewed by iris (Reviewer).

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PR: https://git.openjdk.org/jtreg/pull/124