Use RevisionVersion field instead of CreationTimestamp to decide whic…

…h MS is new/old

The CreationTimestamp is not always the referential value for comparision.
The time.Time.Before method does not always return true when it should.
Leading to new and old MSs to be selected in an oposite way.
Using the RevisionVersion for comparision is more precise and it solves
the case where CreationTimestamp fields of both MSs has the same value.

From observation the following machineset CreationTimestamps led to incorrect ordering of MSs:
item[0]: ResourceVersion:"78", CreationTimestamp:v1.Time{Time:time.Time{wall:0x0, ext:63684460660, loc:(*time.Location)(0x2cb5040)}}
item[1]: ResourceVersion:"82", CreationTimestamp:v1.Time{Time:time.Time{wall:0x0, ext:63684460661, loc:(*time.Location)(0x2cb5040)}}

Even though item[1]'s ext field has higher value than item[0]'s ext field,
item[1] was selected by time.Time.Before as old MS instead of new one.

pkg/controller/machinedeployment/machinedeployment_controller_test.go

@@ -17,6 +17,7 @@ limitations under the License.
 package machinedeployment
 
 import (
+	"strconv"
 	"testing"
 	"time"
 
@@ -153,7 +154,16 @@ func TestReconcile(t *testing.T) {
 	// Wait for the new MachineSet to get scaled up and set .Status.Replicas and .Status.AvailableReplicas
 	// at each step
 	var newMachineSet, oldMachineSet *machinev1beta1.MachineSet
-	if machineSets.Items[0].CreationTimestamp.Before(&machineSets.Items[1].CreationTimestamp) {
+	resourceVersion0, err0 := strconv.Atoi(machineSets.Items[0].ResourceVersion)
+	resourceVersion1, err1 := strconv.Atoi(machineSets.Items[1].ResourceVersion)
+	if err0 != nil {
+		t.Fatalf("Unable to convert MS %q ResourceVersion to a number: %v", machineSets.Items[0].Name, err0)
+	}
+	if err1 != nil {
+		t.Fatalf("Unable to convert MS %q ResourceVersion to a number: %v", machineSets.Items[1].Name, err1)
+	}
+
+	if resourceVersion0 > resourceVersion1 {
 		newMachineSet = &machineSets.Items[0]
 		oldMachineSet = &machineSets.Items[1]
 	} else {