The error returned to users when a load_connection(s)/set_logging call
fails due to D-Bus policy denial is a bit obscure:

  $ nmcli general logging level debug
  Error: failed to set logging: Rejected send message, 4 matched rules;
  type="method_call", sender=":1.233" (uid=1001 pid=27225 comm="nmcli
  general logging level debug ")
  interface="org.freedesktop.NetworkManager" member="SetLogging" error
  name="(unset)" requested_reply="0" destination=":1.207" (uid=0
  pid=25793 comm="/usr/sbin/NetworkManager --no-daemon ")

Convert it to a more comprehensible:

  $ nmcli general logging level debug
  Error: failed to set logging: access denied

https://bugzilla.redhat.com/show_bug.cgi?id=1362542