Enable seccomp by default for unprivileged users.

Enable seccomp by default for unprivileged users.

In contrast to what the comment above the line disabling it said,
it seems to work just fine.  It also is needed on current kernels
(until Eric's patch hits upstream) to prevent unprivileged containers
from hosing fuse filesystems they inherit.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>