RFR: 8259493: [test] Use HexFormat instead of adhoc hex utilities in network code and locale SoftKeys

[Roger Riggs]

Cleanup of tests test/jdk/java/net and test/jdk/sun/net that format hexadecimal strings to use java.util.HexFormat methods.
Also in tests test/jdk/java/util/Locale/SoftKeys.

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Commit messages:
 - 8259493: [test] Use HexFormat instead of adhoc hex utilities in network code and locale SoftKeys

Changes: https://git.openjdk.java.net/jdk/pull/2009/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2009&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8259493
  Stats: 75 lines in 5 files changed: 2 ins; 63 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2009.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2009/head:pull/2009

PR: https://git.openjdk.java.net/jdk/pull/2009