[Test] Fix parsing bug with scontrol output for dumping JOB output and command timeouts

[himani2411]

Description of changes

Adding checks for filepath before we output or read the file so that we avoid hanging of the command when we have non-printable characters.

• Use shelex quote for all filepath to prevent unexpected behavior from special characters from scontrol
• Check for / (absolute path), and contains only printable characters. This catches empty strings, non-printable characters (null bytes, carriage returns), and relative/garbage paths.

Adding OS level timeout so that we can escape the test if PTY or Bash shell doesnt timeout or close the session cleanly.

• OS-level timeout command sends SIGTERM after 60 seconds, regardless of PTY/login shell/Fabric behavior
• Fabric's SSH timeout set to 70 seconds as a backup, giving the OS timeout 10 seconds to kill the process before the SSH layer intervenes

Tests

• test_gb200

References

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