Add switch to push data to urandom

[ZAlexanderV]

a lot of applications use /dev/urandom as source of entropy. Offer to add switch and push data to /dev/urandom.
Any comments @manuel-domke ?

[thillux]

In current Linux kernels, /dev/random and /dev/urandom use the same input pool and the same per-cpu RNGs. It is therefore totally ok, to write entropy to /dev/random, when /dev/urandom is used mostly. This entropy will "reach" /dev/urandom.