Add GC unit tests

Adds unit tests covering the problematic scenarios identified
around conflicting data in child owner references

                      Before   After
package level         51%      68%
garbagecollector.go   60%      75%
graph_builder.go      50%      81%
graph.go              50%      68%

Added/improved coverage of key functions that had lacking unit test coverage:

* attemptToDeleteWorker
* attemptToDeleteItem
* processGraphChanges (added coverage of all added code)

Kubernetes-commit: e491c3bc7056530d82590d95f0af0e8c4d8dded5

tools/record/fake.go

@@ -27,17 +27,29 @@ import (
 // thrown away in this case.
 type FakeRecorder struct {
 	Events chan string
+
+	IncludeObject bool
+}
+
+func objectString(object runtime.Object, includeObject bool) string {
+	if !includeObject {
+		return ""
+	}
+	return fmt.Sprintf(" involvedObject{kind=%s,apiVersion=%s}",
+		object.GetObjectKind().GroupVersionKind().Kind,
+		object.GetObjectKind().GroupVersionKind().GroupVersion(),
+	)
 }
 
 func (f *FakeRecorder) Event(object runtime.Object, eventtype, reason, message string) {
 	if f.Events != nil {
-		f.Events <- fmt.Sprintf("%s %s %s", eventtype, reason, message)
+		f.Events <- fmt.Sprintf("%s %s %s%s", eventtype, reason, message, objectString(object, f.IncludeObject))
 	}
 }
 
 func (f *FakeRecorder) Eventf(object runtime.Object, eventtype, reason, messageFmt string, args ...interface{}) {
 	if f.Events != nil {
-		f.Events <- fmt.Sprintf(eventtype+" "+reason+" "+messageFmt, args...)
+		f.Events <- fmt.Sprintf(eventtype+" "+reason+" "+messageFmt, args...) + objectString(object, f.IncludeObject)
 	}
 }