create: add a quiet flag

If set, then fds 0,1,2 will be redirected while the creation
template is executed.

Note, as Dwight has pointed out, if fd 0 is redirected, then if
templates ask for input there will be a problem.  We could simply
not redirect fd 0, or we could require that templates work without
interaction.  I'm assuming here that we want to do the latter, but
I'm open to changing that.

Reported-by: "S.Çağlar Onur" <caglar@10ur.org>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>