update-ipblocklists: Fix loading new blocklists after update

update-ipblocklists: Fix loading new blocklists after update

* The script needs to run with root permissions in order to
  do the ipset operations. So remove code to drop the permissions
  on startup.

* Adjust execute calls to use the proper functions from
  general functions.

* Add some code to set the correct ownership (nobody:nobody) for
  changed files during script runtime.

Fixes #13072.

Signed-off-by: Stefan Schantl <stefan.schantl@ipfire.org>