guest: Add default RNG to s390x guests

As long as it's supported by both QEMU and the guest OS,
there's really no reason not to add it.

Reviewed-by: Cole Robinson <crobinso@redhat.com>
Signed-off-by: Andrea Bolognani <abologna@redhat.com>

tests/cli-test-xml/compare/virt-install-s390x-cdrom-KVMIBM.xml

@@ -42,6 +42,9 @@
       <model type="virtio"/>
     </video>
     <watchdog model="diag288" action="reset"/>
+    <rng model="virtio">
+      <backend model="random">/dev/urandom</backend>
+    </rng>
     <panic model="s390"/>
   </devices>
 </domain>

tests/cli-test-xml/compare/virt-install-s390x-cdrom.xml

@@ -37,5 +37,8 @@
     <console type="pty">
       <target type="sclp"/>
     </console>
+    <rng model="virtio">
+      <backend model="random">/dev/urandom</backend>
+    </rng>
   </devices>
 </domain>

tests/cli-test-xml/compare/virt-install-s390x-graphics.xml

@@ -35,5 +35,8 @@
     <video>
       <model type="virtio"/>
     </video>
+    <rng model="virtio">
+      <backend model="random">/dev/urandom</backend>
+    </rng>
   </devices>
 </domain>

tests/cli-test-xml/compare/virt-install-s390x-headless.xml

@@ -29,5 +29,8 @@
     <console type="pty">
       <target type="sclp"/>
     </console>
+    <rng model="virtio">
+      <backend model="random">/dev/urandom</backend>
+    </rng>
   </devices>
 </domain>

virtinst/guest.py

@@ -828,6 +828,7 @@ class Guest(XMLBuilder):
             return
         if not (self.os.is_x86() or
                 self.os.is_arm_machvirt() or
+                self.os.is_s390x() or
                 self.os.is_pseries()):
             return