New FreeBSD/EC2 AMIs: "small" flavour

Hi cloudy people,

I'm planning on adding a new flavour of FreeBSD/EC2 AMIs: "Small" AMIs,
which are the standard FreeBSD "base" images minus some bits which are
optional or generally less likely to be useful for production systems:

* They don't have kernel or world debug symbols,
* They don't have FreeBSD tests,
* They don't have 32-bit libraries,
* They don't have LLDB,
* They don't have the Amazon SSM Agent pre-installed,
* They don't default to installing the awscli at first boot.

Phabricator review: https://reviews.freebsd.org/D46509

I'm planning on committing this in a few days (aka before this week's
snapshot builds); if you have any feedback on the "smallification" I
did above, please let me know.

-- 
Colin Percival
FreeBSD Release Engineering Lead & EC2 platform maintainer
Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid