Prevent the death of other tasks when one fails

arkindex/ponos/migrations/0006_task_worker_run.py

arkindex/ponos/models.py

arkindex/process/builder.py

arkindex/process/managers.py

arkindex/process/models.py

arkindex/process/signals.py

arkindex/process/tests/test_processes.py

arkindex/process/tests/test_signals.py

arkindex/process/tests/test_templates.py

arkindex/process/tests/test_workerruns.py