Update Wire Protocol documentation to use Python 3

Updates the wire protocol documentation demonstration to use xmlrpc.client, as
this was factored out of xmlrpclib in Python 3 - you can no longer import
xmlrpclib in Python 3, you must use xmlrpc.(client|server).

Signed-off-by: Colin Barr <[email protected]>

Author: Colin Barr

xen-api/wire-protocol.md

@@ -227,11 +227,11 @@ First, initialise python and import the library `xmlrpclib`:
 
     $ python
     ...
-    >>> import xmlrpclib
+    >>> import xmlrpc.client
 
 Create a python object referencing the remote server:
 
-    >>> xen = xmlrpclib.Server("https://localhost:443")
+    >>> xen = xmlrpc.client.Server("https://localhost:443")
 
 Acquire a session reference by logging in with a username and password
 (error-handling ommitted for brevity; the session reference is returned