Add isMigrating property to the allocation model

ui/app/models/allocation.js

@@ -41,6 +41,7 @@ export default Model.extend({
   }),
 
   isRunning: equal('clientStatus', 'running'),
+  isMigrating: attr('boolean'),
 
   // When allocations are server-side rescheduled, a paper trail
   // is left linking all reschedule attempts.

ui/app/serializers/allocation.js

@@ -40,6 +40,8 @@ export default ApplicationSerializer.extend({
 
     hash.RescheduleEvents = (hash.RescheduleTracker || {}).Events;
 
+    hash.IsMigrating = (hash.DesiredTransition || {}).Migrate;
+
     // API returns empty strings instead of null
     hash.PreviousAllocationID = hash.PreviousAllocation ? hash.PreviousAllocation : null;
     hash.NextAllocationID = hash.NextAllocation ? hash.NextAllocation : null;