setup.sh: set permissions to passwd file when created

Fixing #104 
I find out that in setup.sh we haven't specified any permissions for .htpasswd, so everyone could read. I also fixed permissions in the current ongoing file.
I think that all /etc/rivoluz files are well restricted. Instead we have no so strong permissions in /var/lib/rivoluz where many files can be read by everyone. IMHO it's not a problem because apart from passwords, all other informations are quite public. So I decided to fix only .htpasswd permissions.