Use /dev/random instead of /dev/urandom

/dev/random should be used for crypto-grade RNG.

To make sure use of /dev/random doesn't stall due to lack of entropy, install haveged which fills the entropy pool with sources such as network traffic, key strokes, etc.

On branch master
Your branch is up-to-date with 'origin/master'.

Changes to be committed:
	modified:   setup/dns.sh
	modified:   setup/system.sh
	modified:   setup/webmail.sh
The comment above this line talks specifically about `/dev/urandom` instead of `/dev/random`, so you'll at least want to update the comment too.