sysutils/nut*: Make nut file ownership fixes optional with default enabled

The nut file ownership fixups due to the UID/GID change from uucp/uucp
to nut/nut may not be desireable for all users. Some users with custom
file ownership may wish ownership to remain untouched. This revision
to the nut family of ports/packages allows users to optionally disable
automatic fixup of nut file ownership.

While at it, rather than use a hardcoded string for user/group ownerships,
use the set parameters in Makefile.

PR: 269497
suggested by: dvl