refactor if-else to switch statement (apache#731)

Closes: apache#731

Signed-off-by: qzhu <[email protected]>

Author: targetoee

pkg/scheduler/objects/application.go

@@ -1687,11 +1687,12 @@ func (sa *Application) decUserResourceUsage(resource *resources.Resource, remove
 
 // Track used and preempted resources
 func (sa *Application) trackCompletedResource(info *Allocation) {
-	if info.IsPreempted() {
+	switch {
+	case info.IsPreempted():
 		sa.updatePreemptedResource(info)
-	} else if info.IsPlaceholder() {
+	case info.IsPlaceholder():
 		sa.updatePlaceholderResource(info)
-	} else {
+	default:
 		sa.updateUsedResource(info)
 	}
 }