When creating a new datastore the basedir is only owned by the backup
user if it did not exist beforehand (create_path chowns only if it
creates the directory), and returns false if it did not create the
directory).
This improves the experience when adding a new datastore on a fresh
disk or existing directory (not owned by backup) - backups/pulls can
be run instead of terminating with EPERM.
Tested on my local testinstall with a new disk, and a existing directory:
Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>