Testnode: Expose log folder

Profiles for https://lab.nexedi.com/nexedi/erp5/merge_requests/948

Testnode expose the log folder for test suite, so that they can expose more logs and snapshots.

Because these can be big, we expose a new "keep-log-days" option so that we can se shorter delay for test nodes running software release tests.

Another important visible change is that testnode now automatically restart when configuration is changed.