tests: Replaces images used with agnhost (part 2)

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:

- net
- netexec
- nettest
- webhook

test/utils/image/manifest.go

@@ -105,8 +105,6 @@ var (
 const (
 	// CRDConversionWebhook image
 	CRDConversionWebhook = iota
-	// AdmissionWebhook image
-	AdmissionWebhook
 	// Agnhost image
 	Agnhost
 	// Alpine image
@@ -163,12 +161,6 @@ const (
 	MounttestUser
 	// Nautilus image
 	Nautilus
-	// Net image
-	Net
-	// Netexec image
-	Netexec
-	// Nettest image
-	Nettest
 	// Nginx image
 	Nginx
 	// NginxNew image
@@ -217,8 +209,7 @@ const (
 func initImageConfigs() map[int]Config {
 	configs := map[int]Config{}
 	configs[CRDConversionWebhook] = Config{e2eRegistry, "crd-conversion-webhook", "1.13rev2"}
-	configs[AdmissionWebhook] = Config{e2eRegistry, "webhook", "1.15v1"}
-	configs[Agnhost] = Config{e2eRegistry, "agnhost", "2.0"}
+	configs[Agnhost] = Config{e2eRegistry, "agnhost", "2.1"}
 	configs[Alpine] = Config{dockerLibraryRegistry, "alpine", "3.7"}
 	configs[AuthenticatedAlpine] = Config{gcAuthenticatedRegistry, "alpine", "3.7"}
 	configs[APIServer] = Config{e2eRegistry, "sample-apiserver", "1.10"}
@@ -245,9 +236,6 @@ func initImageConfigs() map[int]Config {
 	configs[Mounttest] = Config{e2eRegistry, "mounttest", "1.0"}
 	configs[MounttestUser] = Config{e2eRegistry, "mounttest-user", "1.0"}
 	configs[Nautilus] = Config{e2eRegistry, "nautilus", "1.0"}
-	configs[Net] = Config{e2eRegistry, "net", "1.0"}
-	configs[Netexec] = Config{e2eRegistry, "netexec", "1.1"}
-	configs[Nettest] = Config{e2eRegistry, "nettest", "1.0"}
 	configs[Nginx] = Config{dockerLibraryRegistry, "nginx", "1.14-alpine"}
 	configs[NginxNew] = Config{dockerLibraryRegistry, "nginx", "1.15-alpine"}
 	configs[Nonewprivs] = Config{e2eRegistry, "nonewprivs", "1.0"}