initchroot: use tee to log to $ROOTDIR.log

initchroot: use tee to log to $ROOTDIR.log

Make a named pipe (which we clean up on exit or script death), set our
stdout/stderr to it, and pipe it tee so we can see what's happening and
log at the same time.

Signed-off-by: Andres Salomon <dilinger@debian.org>