templates/ubuntu: support netplan in newer releases by default

If netplan is present in the container, configure default networking
with neplan instead of ifupdown. Also, do not install ifupdown when
boostrapping minbase variant, unless using currently support
non-netplan releases (trusty, zenial, zesty).

Signed-off-by: Dimitri John Ledkov <xnox@ubuntu.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>

templates/lxc-ubuntu.in

@@ -92,7 +92,15 @@ configure_ubuntu()
     password=$5
 
     # configure the network using the dhcp
-    cat <<EOF > $rootfs/etc/network/interfaces
+    if [ -d $rootfs/etc/netplan ]; then
+        cat <<EOF > $rootfs/etc/netplan/10-lxc.yaml
+network:
+  ethernets:
+    eth0: {dhcp4: true}
+  version: 2
+EOF
+    else
+        cat <<EOF > $rootfs/etc/network/interfaces
 # This file describes the network interfaces available on your system
 # and how to activate them. For more information, see interfaces(5).
 
@@ -103,6 +111,7 @@ iface lo inet loopback
 auto eth0
 iface eth0 inet dhcp
 EOF
+    fi
 
     # set the hostname
     cat <<EOF > $rootfs/etc/hostname
@@ -366,7 +375,13 @@ download_ubuntu()
         debootstrap_parameters="$debootstrap_parameters --variant=$variant"
     fi
     if [ "$variant" = 'minbase' ]; then
-        packages_template="${packages_template},sudo,ifupdown,isc-dhcp-client"
+        packages_template="${packages_template},sudo"
+        # Newer releases use netplan, EOL releases not supported
+        case $release in
+          trusty|xenial|zesty)
+                packages_template="${packages_template},ifupdown,isc-dhcp-client"
+                ;;
+        esac
     fi
 
     echo "Installing packages in template: ${packages_template}"