testing: Rename interfaces and bridges so they are easier to identify

This simplifies capturing traffic with Wireshark on the host as each of
the guest's interfaces is clearly identified.
The three bridges were previously numbered starting from 0, this scheme
is restored here.

testing/config/kvm/sun.xml

@@ -38,12 +38,14 @@
     <interface type='network'>
       <mac address='52:54:00:77:43:ea'/>
       <source network='vnet1'/>
+      <target dev='sun-eth0'/>
       <model type='virtio'/>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
     </interface>
     <interface type='network'>
       <mac address='52:54:00:0f:97:db'/>
       <source network='vnet3'/>
+      <target dev='sun-eth1'/>
       <model type='virtio'/>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
     </interface>