sysutils/nut*: Fix nut file access

Preexisting nut files will have uucp group permissions, which will no
longer be available to nut because it runs under its own GID. For the
time being add code to nut_prestart() adjusting the ownership of the
files to UID nut and GID nut.

This code should be removed approximately a year from now as it is
expected that most if not all nut installations will have correct file
ownership by then.

While here, also fix nut.newsyslog to refer to the new nut UID/GID.

Reported by: avg, Mathieu <sigsys@gmail.com>
Fixes: 02c038c8cc15