Change ComputerDriver.legacy_nwinfo to raise by default.

This makes non-updated hypervisors visible by grepping for 'def
legacy_nwinfo' rather than only the updated ones being visible, and
when new hypervisors are added, it will be clear whether they use the
legacy format or not.

Out of tree hypervisors will be broken by this, but the fix is
trivial::

def legacy_nwinfo(self):
    # XXX TODO Update to use the non-legacy format.
    return True

Change-Id: If5b461bc5d8e8dc21de3ca9cf521e7b341724900

nova/virt/baremetal/driver.py

@@ -166,6 +166,9 @@ class BareMetalDriver(driver.ComputeDriver):
         # TODO(deva): define the version properly elsewhere
         return 1
 
+    def legacy_nwinfo(self):
+        return True
+
     def list_instances(self):
         l = []
         ctx = nova_context.get_admin_context()