call_hook: honor $STOP_ON_ERROR when an executed hook sets task_error

[peturingi]

Debian bug: https://bugs.debian.org/1121552

A hook that runs as a separate process (not a .sh sourced hook) executes in a subshell. If it calls task_error CODE 1 with CODE > $STOP_ON_ERROR, stop_fai_installation is invoked inside the subshell; in most environments die then only replaces the subshell (e.g. exec bash -i under nfsroot) or only affects the subshell's state, so the parent FAI process continues running subsequent tasks.

The fix re-reads $LOGDIR/task_error after an executed hook returns and calls stop_fai_installation from the parent shell if the threshold has been crossed. Sourced .sh hooks already run in the parent shell and need no change.

[Copilot]

Pull request overview

This PR fixes a failure mode where an executed (non-sourced) hook runs in a subshell and can’t reliably stop the parent FAI process when it triggers task_error above $STOP_ON_ERROR. The change makes the parent shell re-check the global task error state after an executed hook returns and stops the installation from the parent context when needed.

Changes:

• After running an executed hook ($hook.$class), re-read $LOGDIR/task_error.
• If the recorded error exceeds $STOP_ON_ERROR, call stop_fai_installation from the parent shell.

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