LXC: Set default driver for image backed filesystems

If no explicit driver is set for an image backed filesystem,
set it to use the loop driver (if raw) or nbd driver (if
non-raw)
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

src/lxc/lxc_controller.c

@@ -462,6 +462,14 @@ static int virLXCControllerSetupLoopDevices(virLXCControllerPtr ctrl)
         if (fs->type != VIR_DOMAIN_FS_TYPE_FILE)
             continue;
 
+        if (fs->fsdriver == VIR_DOMAIN_FS_DRIVER_TYPE_DEFAULT) {
+            if (fs->format == VIR_STORAGE_FILE_RAW ||
+                fs->format == VIR_STORAGE_FILE_NONE)
+                fs->fsdriver = VIR_DOMAIN_FS_DRIVER_TYPE_LOOP;
+            else
+                fs->fsdriver = VIR_DOMAIN_FS_DRIVER_TYPE_NBD;
+        }
+
         if (fs->fsdriver == VIR_DOMAIN_FS_DRIVER_TYPE_LOOP) {
             if (fs->format != VIR_STORAGE_FILE_RAW &&
                 fs->format != VIR_STORAGE_FILE_NONE) {