3scale system-storage backup fails with a "Permission denied" error when the system-storage directory group is root

Issue

• When using the 3scale documentation to backup system-storage, the command fails with a "Permisison denied" error if the directory group of /opt/system/public/system in system-storage is root

  $ oc rsync $(oc get pods -l 'deploymentConfig=system-app' -o json | jq '.items[0].metadata.name' -r):/opt/system/public/system ./local/dir
  receiving incremental file list
  
  sent 8 bytes  received 89 bytes  64.67 bytes/sec
  total size is 0  speedup is 0.00
  Defaulted container "system-master" out of: system-master, system-provider, system-developer
  rsync: link_stat "/opt/system/public/system" failed: Permission denied (13)
  command terminated with exit code 23
  rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1659) [Receiver=3.1.3]
  rsync: [Receiver] write error: Broken pipe (32)
  error: exit status 23