RFR: 8265918: java/io/Console/CharsetTest.java failed with "expect: spawn id exp6 not open"

[Naoto Sato]

This new regression test was introduced with the Console::charset(), but it fails on ubuntu platforms assuming its locales/encoding incorrectly. To not make false-alarm/noise on test runs, this fix minimizes the tests not depending on the underlying OS's environment variables.

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Commit messages:
 - 8265918: java/io/Console/CharsetTest.java failed with "expect: spawn id exp6 not open"

Changes: https://git.openjdk.java.net/jdk/pull/3768/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3768&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8265918
  Stats: 13 lines in 2 files changed: 0 ins; 11 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3768.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3768/head:pull/3768

PR: https://git.openjdk.java.net/jdk/pull/3768