Use printf in favor of echo for reproducibility

[mouadino]

In my machine, echo will lead to literally having \n in /etc/exports file which will lead the nfs server to fail starting, this is due to the echo version that I have locally, while printf doesn't have this issue as explained here: https://stackoverflow.com/questions/8467424/echo-newline-in-bash-prints-literal-n

[tonivdv]

Thanks.