MFC r316548:

Quiet 450.status-security when *_inline="YES"

Previously, 450.status-security would always set rc=3 in inline mode,
because it doesn't know whether "periodic security" is going to find
anything interesting. But this annoyingly results in daily reports that
simply say "Security check: \n\n-- End of daily output --".

This change fixes that by testing whether "periodic security" printed
anything, and setting 450.status-security's exit status to 3 if it did. An
alternative would be to change the exit status of periodic(8) to be the
worst of its scripts' exit statuses, but that would be a more intrusive
change.

Reviewed by: brian
Differential Revision: https://reviews.freebsd.org/D10267

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Make the period of each periodic security script configurable.

There are now six additional variables
weekly_status_security_enable
weekly_status_security_inline
weekly_status_security_output
monthly_status_security_enable
monthly_status_security_inline
monthly_status_security_output
alongside their existing daily counterparts. They all have the same
default values.

All other "daily_status_security_${scriptname}_${whatever}"
variables have been renamed to "security_status_${name}_${whatever}".
A compatibility shim has been introduced for the old variable names,
which we will be able to remove in 11.0-RELEASE.

"security_status_${name}_enable" is still a boolean but a new
"security_status_${name}_period" allows to define the period of
each script. The value is one of "daily" (the default for backward
compatibility), "weekly", "monthly" and "NO".

Note that when the security periodic scripts are run directly from
crontab(5) (as opposed to being called by daily or weekly periodic
scripts), they will run unless the test is explicitely disabled with a
"NO", either for in the "_enable" or the "_period" variable.

When the security output is not inlined, the mail subject has been
changed from "$host $arg run output" to "$host $arg $period run output".
For instance:
myfbsd security run output -> myfbsd security daily run output
I don't think this is considered as a stable API, but feel free to
correct me if I'm wrong.

Finally, I will rearrange periodic.conf(5) and default/periodic.conf
to put the security options in their own section. I left them in
place for this commit to make reviewing easier.

Reviewed by: hackers@