RFR: JDK-8315214: Do not run sun/tools/jhsdb tests concurrently

[Matthias Baesken]

The sun/tools/jhsdb tests have issues when we run them concurrently .
So add a related config to TEST.root.

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Commit messages:
 - JDK-8315214

Changes: https://git.openjdk.org/jdk/pull/15469/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15469&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315214
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15469.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15469/head:pull/15469

PR: https://git.openjdk.org/jdk/pull/15469