lib.xo.xo_cli: don't pass --json argument for 'list-objects' command

[semarie]

on xo-cli cli command, --json argument isn't valid on 'list-objects' commands, so avoid to pass it. The output is JSON anyway for this command.

instead, --property is used to filter the property returned.

  xo-cli list-objects [--<property>]… [<property>=<value>]...
    Returns a list of XO objects.

   --<property>
      Restricts displayed properties to those listed.

  xo-cli <command> [--json] [<name>=<value>]...
    Executes a command on the current XO instance.

[semarie]

in the current (faulty) behavior, we are returning [{}] the list of objects, with only the json property if it exists (it usually doesn't, so the object is empty)

list-objects is used in xo_object_exists() method. but as the function returns if the object exists, it was fine before and it is still fine now.