RFR: 8275007: Java fails to start with null charset if LC_ALL is set to certain locales

[Naoto Sato]

Please review the subject fix. In light of JEP400, Java runtime can/should start in UTF-8 charset if the underlying native encoding is not supported.

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Commit messages:
 - Use UTF-8 if jnuEncoding is not supported
 - Utilized 2-arg Charset.forName()
 - 8275007: Java fails to start with null charset if LC_ALL is set to certain

Changes: https://git.openjdk.java.net/jdk/pull/6282/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6282&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275007
  Stats: 22 lines in 3 files changed: 4 ins; 7 del; 11 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6282.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6282/head:pull/6282

PR: https://git.openjdk.java.net/jdk/pull/6282