Allow freebsd-update fetch to run in a non-interactive tty

[• rodrigc]

Summary

The freebsd-update fetch command cannot run in a non-interactive tty.
This makes running freebsd-update via automation difficult.
The freebsd-update cron command can run via automation, but it adds
a random delay from 1 to 3600 seconds. This is inconvenient for automation.

These issues were discovered by Ahmed Kamal <[e-mail]>, who is helping
with Saltstack devops automation for the jenkins.freebsd.org cluster.

[cperciva]

I'd much prefer to see a --not-a-dumb-cron-job option added for this. A large network doing synchronized updates can generate a lot of traffic, and I'm not confident that users will be aware of the risks.

[allanjude]

I addressed this in my patch here: D1550

It allows a user to 'force' the fetch to continue by specifying -f

My patch was designed to actually add another sanity check (stop you doing a minor patch when you have not finished a previous upgrade), but the -f overrides either check.

[• rodrigc]

I'm OK with D1550. It does the job.