improve output during Dropbear start

We have output for each step, so we can see which of them takes so long. Actually, makeSureLastlogExists takes very long although it simply touches a file. I previously suspected that generation of SSH keys would be the culprit.
use 'cp -a' for copyFilesToNfsRoot

... because a Copy task doesn't play well with symlinks: It creates a normal file instead of the link. This means that our rootfs is 4 times the size and sometimes behaves weird (e.g. one changes a file in /etc/init.d/, but the old file from /etc/rc.d is used. Usually, there would be a link in /etc/rc.d to avoid that.)