RFR: 8299779: Test tools/jpackage/share/jdk/jpackage/tests/MainClassTest.java timed out

[Alexander Matveev]

- Fixed by increasing test timeout. Fix verified on host which reproduced issue.

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Commit messages:
 - 8299779: Test tools/jpackage/share/jdk/jpackage/tests/MainClassTest.java timed out

Changes: https://git.openjdk.org/jdk/pull/12896/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12896&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299779
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12896.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12896/head:pull/12896

PR: https://git.openjdk.org/jdk/pull/12896