RFR: 2415: Update GitCommits::close to make sure it terminates all processes when an exception is thrown [v2]

[Zhao Song]

> As Pavel pointed out in the pull request of [SKARA-2410](https://bugs.openjdk.org/browse/SKARA-2410)(https://github.com/openjdk/skara/pull/1697), with current implementation , GitCommits::close may have created multiple processes and only destroy one of them.
> 
> As Erik and Pavel suggested, we should make sure close() is called on each process.

Zhao Song has updated the pull request incrementally with one additional commit since the last revision:

  review comment

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Changes:
  - all: https://git.openjdk.org/skara/pull/1699/files
  - new: https://git.openjdk.org/skara/pull/1699/files/f1d39f11..2a9da277

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=skara&pr=1699&range=01
 - incr: https://webrevs.openjdk.org/?repo=skara&pr=1699&range=00-01

  Stats: 11 lines in 1 file changed: 4 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/skara/pull/1699.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1699/head:pull/1699

PR: https://git.openjdk.org/skara/pull/1699