Rename don't recreate repos on move (Fix #12355)

If a sysadmin properly moves the omero.data.dir to
new location via:

```
  bin/omero config omero.data.dir NEW
  mv OLD NEW
```

then there's no reason that a new repository should
be created. Instead, now a WARN log statement is
printed and the new value should be visible via
`bin/omero fs repos`. Imports of files from before
and after the renaming should work identically.