Don't leak file descriptors when setting up daemon output

When a daemon's output is configured using “utils.SetupDaemonFDs”, the
function must use dup2(2). Unfortunately the code didn't close the
original file descriptors, leaking them in the process.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>