Add function for listing native threads to eventlet backdoor

The eventlet backdoor has a 'pgt' function for listing green
threads and their stack traces. This adds a new 'pnt' function
for doing the same with native threads.

Change-Id: If6dcfd8dde61c96adfc6e052e5ec7db82914cd55
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Merge "Add function for listing native threads to eventlet backdoor"