RFR: 8285616: [macos] Incorrect path for launcher-as-service.txt in .cfg file

[Alexey Semenyuk]

- Replace `System.getProperty("java.io.tmpdir")` call with hardcoded `/tmp` string to get root folder for test files.
- Fix test cleanup - the test didn't delete test files upon completion

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Commit messages:
 - 8285616: [macos] Incorrect path for launcher-as-service.txt in .cfg file

Changes: https://git.openjdk.java.net/jdk/pull/8563/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8563&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285616
  Stats: 5 lines in 1 file changed: 1 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8563.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8563/head:pull/8563

PR: https://git.openjdk.java.net/jdk/pull/8563