tests: Replaces images used with agnhost (part 1)

Quite a few images are only used a few times in a few tests. Thus,
the images are being centralized into the agnhost image, reducing
the number of images that have to be pulled and used.

This PR replaces the usage of the following images with agnhost:

- fakegitserver
- hostexec
- liveness
- logs-generator
- no-snat-test
- no-snat-test-proxy
- port-forward-tester

test/e2e/common/util.go

@@ -48,29 +48,28 @@ var CurrentSuite Suite
 // only used by node e2e test.
 // TODO(random-liu): Change the image puller pod to use similar mechanism.
 var CommonImageWhiteList = sets.NewString(
+	imageutils.GetE2EImage(imageutils.Agnhost),
 	imageutils.GetE2EImage(imageutils.AuditProxy),
 	imageutils.GetE2EImage(imageutils.BusyBox),
 	imageutils.GetE2EImage(imageutils.EntrypointTester),
 	imageutils.GetE2EImage(imageutils.IpcUtils),
-	imageutils.GetE2EImage(imageutils.Liveness),
 	imageutils.GetE2EImage(imageutils.Mounttest),
 	imageutils.GetE2EImage(imageutils.MounttestUser),
 	imageutils.GetE2EImage(imageutils.Netexec),
 	imageutils.GetE2EImage(imageutils.Nginx),
 	imageutils.GetE2EImage(imageutils.ServeHostname),
 	imageutils.GetE2EImage(imageutils.TestWebserver),
-	imageutils.GetE2EImage(imageutils.Hostexec),
 	imageutils.GetE2EImage(imageutils.VolumeNFSServer),
 	imageutils.GetE2EImage(imageutils.VolumeGlusterServer),
 	imageutils.GetE2EImage(imageutils.Net),
 )
 
 type testImagesStruct struct {
+	AgnhostImage      string
 	BusyBoxImage      string
 	GBFrontendImage   string
 	GBRedisSlaveImage string
 	KittenImage       string
-	LivenessImage     string
 	MounttestImage    string
 	NautilusImage     string
 	NginxImage        string
@@ -83,11 +82,11 @@ var testImages testImagesStruct
 
 func init() {
 	testImages = testImagesStruct{
+		imageutils.GetE2EImage(imageutils.Agnhost),
 		imageutils.GetE2EImage(imageutils.BusyBox),
 		imageutils.GetE2EImage(imageutils.GBFrontend),
 		imageutils.GetE2EImage(imageutils.GBRedisSlave),
 		imageutils.GetE2EImage(imageutils.Kitten),
-		imageutils.GetE2EImage(imageutils.Liveness),
 		imageutils.GetE2EImage(imageutils.Mounttest),
 		imageutils.GetE2EImage(imageutils.Nautilus),
 		imageutils.GetE2EImage(imageutils.Nginx),