backends: LXD: don't hardcode eth0

With the ubuntu-22.04 image, the network interface seems
to be named "enp5s0" instead of "eth0". To be compatible
with both old and new releases, consider any non-loopback
interface viable for retrieving an IP address.

spread/lxd.go

@@ -443,9 +443,15 @@ func (p *lxdProvider) address(name string) (string, error) {
 	if err != nil {
 		return "", err
 	}
-	for _, addr := range sjson.State.Network["eth0"].Addresses {
-		if addr.Family == "inet" && addr.Address != "" {
-			return addr.Address, nil
+	for intf, network := range sjson.State.Network {
+		if intf == "lo" {
+			continue
+		}
+		for _, addr := range network.Addresses {
+			debugf("considering interface %v\n", intf)
+			if addr.Family == "inet" && addr.Address != "" {
+				return addr.Address, nil
+			}
 		}
 	}
 	return "", &lxdNoAddrError{name}

tests/lxd/spread.yaml

@@ -4,6 +4,9 @@ backends:
     lxd:
         systems:
             - ubuntu-16.04
+            - ubuntu-18.04
+            - ubuntu-20.04
+            - ubuntu-22.04
 
 path: /home/test