fix up image gc settings in defaults tests

Author: sjenning

pkg/cmd/server/kubernetes/node/node_config_test.go

@@ -72,7 +72,7 @@ func TestKubeletDefaults(t *testing.T) {
 			EnableCustomMetrics:            false,
 			EnableDebuggingHandlers:        true,
 			EnableServer:                   true,
-			EvictionHard:                   "memory.available<100Mi,nodefs.available<10%,nodefs.inodesFree<5%",
+			EvictionHard:                   "memory.available<100Mi,nodefs.available<10%,nodefs.inodesFree<5%,imagefs.available<15%",
 			FileCheckFrequency:             metav1.Duration{Duration: 20 * time.Second}, // overridden
 			HealthzBindAddress:             "127.0.0.1",                                 // disabled
 			HealthzPort:                    10248,                                       // disabled