Print a log message when Nuxeo is shutting down

We would like to add a log message when Nuxeo is shutting down in order to be able to identify this stage of the software where error can happen.

This will be interesting to have such information for production.

This will also be interesting to have such information in our CI when we're looking for errors in server logs during functional testing. Every errors that appear after the request of shutdown are considered as false positive.