Consistently use /dev/urandom instead of /dev/random in scripts and docs

Consistently use /dev/urandom instead of /dev/random in scripts and docs

Unbound code call /dev/urandom (see below)  but various docs and scripts
mention /dev/random which may be confusing.

https://github.com/NLnetLabs/unbound/blob/release-1.9.3/compat/arc4random.c#L107
https://github.com/NLnetLabs/unbound/blob/release-1.9.3/compat/getentropy_linux.c#L251
https://github.com/NLnetLabs/unbound/blob/release-1.9.3/compat/getentropy_osx.c
https://github.com/NLnetLabs/unbound/blob/release-1.9.3/compat/getentropy_solaris.c#L116