bhyve: Add support for VNC autoport

This patch adds support for automatic VNC port assignment for bhyve guests.

Signed-off-by: Roman Bogorodskiy <bogorodskiy@gmail.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

tests/bhyvexml2argvdata/bhyvexml2argv-vnc-autoport.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>
+    <loader readonly="yes" type="pflash">/path/to/test.fd</loader>
+  </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'>
+      <model type='virtio'/>
+      <source bridge="virbr0"/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
+    </interface>
+    <graphics type='vnc' port='-1' autoport='yes'>
+      <listen type='address' address='127.0.0.1'/>
+    </graphics>
+  </devices>
+</domain>