lxd/storage/drivers/btrfs: Clarify fallback in case UUID discovery ti…

…mes out

Signed-off-by: Julian Pelizäus <julian.pelizaeus@canonical.com>

lxd/storage/drivers/driver_btrfs.go

@@ -189,6 +189,8 @@ func (d *btrfs) Create() error {
 		}
 
 		// Confirm that the symlink is appearing (give it 10s).
+		// In case of timeout it falls back to using the volume's path
+		// instead of its UUID.
 		if tryExists(fmt.Sprintf("/dev/disk/by-uuid/%s", devUUID)) {
 			// Override the config to use the UUID.
 			d.config["source"] = devUUID