Add Discovered nodes tab

Adds newly_discovered and maintenance attributes to Ironic node
test data.  The new tab/maintenance column do not appear if
Ironic is not enabled.

Assuming you don't have Ironic installed, you can test by manually
enabling Ironic within NodeClient in tuskar_ui/api/node.py

Change-Id: Ifb5de54fef69c0b2b505a6102b7cc068e343a983