RFR: 8373101: JdkClient and JdkServer test classes ignore namedGroups field

[Matthew Donovan]

This PR updates a couple test utility classes, JdkClient and JdkServer. Theseclasses extend AbstractPeer which contains a `namedGroup` field however, when creating/configuring the objects, the field is ignored. This PR just makes sure to include named groups if they are specified.

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Commit messages:
 - 8373101: JdkClient and JdkServer test classes ignore namedGroups field

Changes: https://git.openjdk.org/jdk/pull/28664/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28664&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373101
  Stats: 25 lines in 2 files changed: 22 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28664.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28664/head:pull/28664

PR: https://git.openjdk.org/jdk/pull/28664