RFR: 8280546: Remove hard-coded 127.0.0.1 loopback address

[Liam Miller-Cushon]

This change replaces hard-coded 127.0.0.1 loopback addresses with `InetAddress.getLoopbackAddress().getHostAddress()`, to allow the tests to work on IPv6-only systems. This matches the approach of previous fixes in [JDK-8220083](https://bugs.openjdk.java.net/browse/JDK-8220083).

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Commit messages:
 - 8280546: Remove hard-coded 127.0.0.1 loopback address

Changes: https://git.openjdk.java.net/jdk/pull/7209/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7209&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280546
  Stats: 5 lines in 2 files changed: 3 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7209.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7209/head:pull/7209

PR: https://git.openjdk.java.net/jdk/pull/7209