generator: Rename 'add_drive_opts' API to 'add_drive'.

By using the once_had_no_optargs flag, this change is backwards
compatible for callers (except Haskell, PHP and GObject as discussed
in earlier commit).

java/examples/InspectVM.java

@@ -35,7 +35,7 @@ public class InspectVM
                 }
             };
 
-            g.add_drive_opts (disk, optargs);
+            g.add_drive (disk, optargs);
 
             // Run the libguestfs back-end.
             g.launch ();