[ZEPPELIN-6258] Improve Process resource management in SparkInterpreterLauncher

[renechoi]

What is this PR for?

This PR improves process resource management in the detectSparkScalaVersion method of SparkInterpreterLauncher.java to prevent process hangs and resource leaks.

Current Issues Fixed:

1. Buffer Overflow Risk: Process stdout was not consumed, potentially causing hangs if spark-submit produces output
2. Indefinite Blocking: No timeout on process.waitFor() could cause indefinite blocking
3. Missing Process Cleanup: Process wasn't explicitly destroyed after use
4. No Exit Value Validation: Process exit status wasn't checked

What type of PR is it?

Improvement

Todos

• [ ] - Code review
• [ ] - CI build verification

What is the Jira issue?

• https://issues.apache.org/jira/browse/ZEPPELIN-6258

How should this be tested?

• Unit test added: testDetectSparkScalaVersionProcessManagement - Verifies the method works correctly with new process management

• Manual testing:

  • Start Zeppelin with Spark interpreter
  • Verify spark-submit processes are properly terminated
  • No zombie processes should remain after interpreter initialization

• CI: All existing tests pass

Screenshots (if appropriate)

N/A

Questions:

• Does the license files need to update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? No

Implementation Details

• Added stdout consumption using IOUtils.copy() to NullOutputStream to prevent buffer overflow
• Implemented 30-second timeout with process.waitFor(30, TimeUnit.SECONDS)
• Added forceful process termination on timeout
• Added exit value logging for better diagnostics
• Ensured process cleanup in finally block with destroyForcibly()
• Moved file reading into try-finally block for better resource management

Benefits

1. Prevents Hangs: Stdout consumption prevents buffer-related process hangs
2. Guaranteed Termination: 30-second timeout ensures process won't block indefinitely
3. Better Diagnostics: Exit value logging helps identify spark-submit failures
4. Resource Safety: Explicit process cleanup prevents zombie processes

[ParkGyeongTae]

Could you please rebase this branch onto master?