Make periodic's output log to files if sendmail is disabled on install

[mykel at mWare.ca]

1) if sendmail is disabled during installation, have periodic's output 
logged to files (per example in 
https://www.freebsd.org/cgi/man.cgi?periodic(8) )

2) make this the default anyway (logging to files), arguably the vast 
majority of systems' reporting is ignored :)
At least now it could be logrotated out!



[22:54.53]  <Myke> AllanJude: will you make the installer smart that if 
the user disables sendmail, that periodic's output will be sent to 
logfiles instead?
[22:55.17]  <AllanJude> not sure how doable that is
[22:57.20]  <Myke> AllanJude: 
https://www.freebsd.org/cgi/man.cgi?periodic(8) <-- see examples
[22:57.55]  <AllanJude> ohh
[22:57.57]  <AllanJude> ok then
[22:58.04]  <AllanJude> should be fairly easy to do then
[23:00.02]  <Myke> AllanJude: I'd argue logging periodic to files should 
become the default since I'm willing to bet 99% of fBSD machines' output 
is ignored.
[23:00.34]  <AllanJude> Myke: that is a reasonable idea for freebsd 12
[23:00.42]  <Myke> :)
[23:00.55]  <AllanJude> want to email that to freebsd-current at freebsd.org
[23:00.57]  <AllanJude> and then i'll do it ;)