bhyve: support random number generator device

Bhyve supports the Virtio RNG interface. It's always using the
/dev/random device and doesn't have any configuration options.

Thus, in XML it's represented as:

  <rng model='virtio'>
    <backend model='random'/>
  </rng>

So extend the bhyve driver to support that and add a set of tests for
this feature.

Signed-off-by: Roman Bogorodskiy <bogorodskiy@gmail.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

tests/bhyvexml2argvdata/bhyvexml2argv-virtio-rnd.args

@@ -0,0 +1,11 @@
+bhyve \
+-c 1 \
+-m 214 \
+-u \
+-H \
+-P \
+-s 0:0,hostbridge \
+-s 2:0,ahci,hd:/tmp/freebsd.img \
+-s 3:0,virtio-net,faketapdev,mac=52:54:00:b9:94:02 \
+-s 4:0,virtio-rnd \
+bhyve

tests/bhyvexml2argvdata/bhyvexml2argv-virtio-rnd.ldargs

@@ -0,0 +1,4 @@
+bhyveload \
+-m 214 \
+-d /tmp/freebsd.img \
+bhyve

tests/bhyvexml2argvdata/bhyvexml2argv-virtio-rnd.xml

@@ -0,0 +1,26 @@
+<domain type='bhyve'>
+  <name>bhyve</name>
+  <uuid>df3be7e7-a104-11e3-aeb0-50e5492bd3dc</uuid>
+  <memory>219136</memory>
+  <vcpu>1</vcpu>
+  <os>
+    <type>hvm</type>
+  </os>
+  <devices>
+    <disk type='file'>
+      <driver name='file' type='raw'/>
+      <source file='/tmp/freebsd.img'/>
+      <target dev='hda' bus='sata'/>
+      <address type='drive' controller='0' bus='0' target='2' unit='0'/>
+    </disk>
+    <interface type='bridge'>
+      <mac address='52:54:00:b9:94:02'/>
+      <model type='virtio'/>
+      <source bridge="virbr0"/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
+    </interface>
+    <rng model='virtio'>
+      <backend model='random'/>
+    </rng>
+  </devices>
+</domain>