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.

python/examples/create_disk.py

@@ -16,7 +16,7 @@ f.close ()
 g.set_trace (1)
 
 # Attach the disk image to libguestfs.
-g.add_drive (output, format = "raw", readonly = 0)
+g.add_drive_opts (output, format = "raw", readonly = 0)
 
 # Run the libguestfs back-end.
 g.launch ()

python/examples/guestfs-python.pod

@@ -8,7 +8,7 @@ guestfs-python - How to use libguestfs from Python
 
  import guestfs
  g = guestfs.GuestFS ()
- g.add_drive ("disk.img", format="raw", readonly=1)
+ g.add_drive_opts ("disk.img", format="raw", readonly=1)
  g.launch ()
 
 =head1 DESCRIPTION

python/examples/inspect_vm.py

@@ -9,7 +9,7 @@ disk = sys.argv[1]
 g = guestfs.GuestFS ()
 
 # Attach the disk image read-only to libguestfs.
-g.add_drive (disk, readonly=1)
+g.add_drive_opts (disk, readonly=1)
 
 # Run the libguestfs back-end.
 g.launch ()