rngd: PB to set up rngd

The *rng-tools* package provides `rngd`, a userspace process that feeds
the Linux entropy pool from additional sources. Notably, it mixes
entropy gathered from hardware random number generators, such as the one
on the BCM2835 SoC on the Raspberry Pi, and the KVM paravirtual random
number generator.

The `rngd.yml` playbook installs *rng-tools* and starts the `rngd`
service.

rngd.yml

@@ -0,0 +1,14 @@
+- hosts: all
+  tasks:
+  - name: ensure rng-tools is installed
+    package:
+      name=rng-tools
+      state=present
+  - name: ensure rngd starts at boot
+    service:
+      name=rngd
+      enabled=yes
+  - name: ensure rngd is running
+    service:
+      name=rngd
+      state=started