add option to globally disable rng device

related to bug: PROD-20139

Change-Id: I32fee91f22e0963ec60de63b4c6e020df92f9f3b

README.rst

           mycluster:
             domain: neco.virt.domain.com
             engine: virt
+            #Option to set rng globaly
+            rng: false
             node:
               ubuntu1:
                 provider: node01.domain.com
                 image: ubuntu.qcow
                 size: medium
                 img_dest: /var/lib/libvirt/ssdimages
+                #Rng defined on node will have higher priority then global one
                 rng:
                   backend: /dev/urandom
                   model: random

salt/control/virt.sls

 
 {%- if cluster.engine == "virt" %}
 
+##Posibility to disable rng device globally for old libvirt version
+{%- if cluster.rng is defined %}
+{%- set rng = cluster.rng %}
+{%- endif %}
+
 {%- for node_name, node in cluster.node.iteritems() %}
 
 {%- if node.name is defined %}
 
 {%- set size = control.size.get(node.size) %}
 
-
 salt_control_virt_{{ cluster_name }}_{{ node_name }}:
   module.run:
   - name: virtng.init
   - start: True
   - disk: {{ size.disk_profile }}
   - nic: {{ size.net_profile }}
-  {%- if node.rng is defined %}
-  - rng: {{ node.rng }}
+  {%- if  node.rng is defined %}
+  - rng: {{  node.rng }}
+  {%- elif rng is defined %}
+  - rng: {{ rng }}
   {%- endif %}
   - kwargs:
       seed: True