fix #12160: root-owned template paths

Fixes https://trac.openmicroscopy.org.uk/ome/ticket/12160 to allow managed repository template paths to start with some root-owned directories.

In `etc/omero.properties` try changing the `omero.fs.repo.path` to something with `//` instead of `/` as a path separator. Imports under such a server should still work fine, the images remaining usable, with those earlier directories owned by root instead of a user.

One can use `bin/omero hql` to check directory ownership with queries like,
```sql
SELECT path || name, details.owner.omeName, details.group.name from OriginalFile where mimetype = 'Directory'
```