RFR: JDK-8268147: need to update reference to testng module for jtreg6

[Jonathan Gibbons]

Please review a test fix to refer to the new name of the TestNG module.

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Commit messages:
 - JDK-8268147: need to update reference to testng module for jtreg6

Changes: https://git.openjdk.java.net/jdk/pull/4325/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4325&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268147
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4325.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4325/head:pull/4325

PR: https://git.openjdk.java.net/jdk/pull/4325