RFR: 8291760: PipelineLeaksFD.java still fails: More or fewer pipes than expected

[Roger Riggs]

Revised test to check and close all of the streams used in the pipeline.

The test now checks the content length and closes each stdout and stderr stream.

The previous technique to redirect stderr to stdout was ineffective because the fd/stream was still created in the parent process.  Created [8291986](https://bugs.openjdk.org/browse/JDK-8291986) ProcessBuilder.redirectErrorStream(true) leaves error stream available to investigate

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Commit messages:
 - 8291760: PipelineLeaksFD.java still fails: More or fewer pipes than expected

Changes: https://git.openjdk.org/jdk/pull/9905/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9905&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8291760
  Stats: 13 lines in 2 files changed: 5 ins; 7 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9905.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9905/head:pull/9905

PR: https://git.openjdk.org/jdk/pull/9905