examples: Use add_drive_opts function in examples.

In libguestfs 1.20, you will be able to use 'add_drive'
instead of 'add_drive_opts' (except in the C bindings).

However until libguestfs 1.20 is the minimum stable version
people will still be using old versions where you have to use
'add_drive_opts'.  This makes the examples confusing.

Therefore continue to use 'add_drive_opts' in the examples
for now.

java/examples/CreateDisk.java

@@ -29,7 +29,7 @@ public class CreateDisk
                     put ("readonly", Boolean.FALSE);
                 }
             };
-            g.add_drive (output, optargs);
+            g.add_drive_opts (output, optargs);
 
             // Run the libguestfs back-end.
             g.launch ();