USB disks attach after rootfs prompt

[Poul-Henning Kamp]

Running:

	FreeBSD 11.0-CURRENT #32 r296137: Sat Feb 27 11:34:01 UTC 2016

I tried "boot -a" and found that USB disks only attach *after* you
enter some root filesystem.

That's not terribly useful.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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FreeBSD committer       | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.