RFR: 8354985: Add unit tests for Executor class from jpackage test lib

[Alexander Matveev]

On Thu, 17 Apr 2025 18:53:16 GMT, Alexey Semenyuk <asemenyuk at openjdk.org> wrote:

> - Add tests covering command output handling in the Executor class
>  - Fix revealed bugs
>  - Add a couple of `Executor.of()` convenience methods
> 
> The test is implemented in a way that it will remain mostly unchanged when Executor supports disabling of stderr and stdout streams.

Looks good.

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Marked as reviewed by almatvee (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/24737#pullrequestreview-2777094666