Use /dev/urandom and /dev/hwrng as a Virtio RNG

Libvirt pre 1.3.4 could not use /dev/urandom as a source of entropy.
Use either /dev/urandom (when we can) or /dev/hwrng (when we cannot) for
our VM. This technically means that /dev/random is not going to be
used as a source anymore.

Change-Id: Ic3257c94ba062ba7eab0892ad1bd39447a4069e9
(cherry picked from commit c91c761ce54e6a16e636e4768b829cbb654b429c)
3 files changed