RFR: 8273617: UninitializedDisplayModeChangeTest.java times out on macOS 12

[Prasanta Sadhukhan]

Test used to timeout even though it seems the test passed..Increased the timeout to a safe value as sometimes it shows elapsed time to timeout > 300secs in macOS in CI and also ensured the wait-time for child process to execute the test is not been waiting endlessly.
Also ensured the original display mode is resetted after the test to prevent affecting following tests.

Tried 100 iterations of the fix on all platforms which is ok

-------------

Commit messages:
 - 8273617: UninitializedDisplayModeChangeTest.java times out on macOS 12

Changes: https://git.openjdk.org/jdk/pull/27365/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27365&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8273617
  Stats: 14 lines in 3 files changed: 6 ins; 5 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/27365.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27365/head:pull/27365

PR: https://git.openjdk.org/jdk/pull/27365