RFR: 8279182: MakeZipReproducible ZipEntry timestamps not localized to UTC

[Andrew Leonard]

MakeZipReproducible was added to enable reproducible building of src.zip. However, as ZipEntry timestamps are a "localized" date with no zone, the specified epoch instant was getting localized in whatever the building timezone was, hence src.zip built from the same source in different zones would differ.
The timestamp should be localized to UTC (like for jar, jmod entries), this PR ensures this.

Signed-off-by: Andrew Leonard <anleonar at redhat.com>

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Commit messages:
 - 8279182: MakeZipReproducible ZipEntry timestamps not localized to UTC

Changes: https://git.openjdk.java.net/jdk/pull/6926/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6926&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8279182
  Stats: 11 lines in 1 file changed: 6 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6926.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6926/head:pull/6926

PR: https://git.openjdk.java.net/jdk/pull/6926