Disable track_instance_changes when in superconductor mode

When configured for superconductor mode, which is the default,
nova-compute can't reach the MQ for nova-scheduler so there is
no point in even enabling the track_instance_changes code since
it's a waste of time as the scheduler will never get the message.

Change-Id: I2662ebd47323428b403d3c2236bec78f1fb1050f
1 file changed