Prevent abnormal timeout values from breaking sync with ironic
I had a case when an operator set the timeout too a abnormally large
value, which caused OverflowError in the timeout clean_up task, which,
in turn, prevented ironic-inspector from ever running node list sync
This change makes two corrections:
* The timeout configuration is limited to 10 years (0 can still be used
to disable the timeout completely).
* Errors in the clean_up task do not prevent the node list sync from