show error when running dockershim

The error returned when running the dockershim is not checked.
When running dockerless, we should show the existing error.

pkg/kubelet/kubelet.go

@@ -316,7 +316,7 @@ func PreInitRuntimeService(kubeCfg *kubeletconfiginternal.KubeletConfiguration,
 
 	switch containerRuntime {
 	case kubetypes.DockerContainerRuntime:
-		runDockershim(
+		if err := runDockershim(
 			kubeCfg,
 			kubeDeps,
 			crOptions,
@@ -324,7 +324,9 @@ func PreInitRuntimeService(kubeCfg *kubeletconfiginternal.KubeletConfiguration,
 			remoteRuntimeEndpoint,
 			remoteImageEndpoint,
 			nonMasqueradeCIDR,
-		)
+		); err != nil {
+			return err
+		}
 	case kubetypes.RemoteContainerRuntime:
 		// No-op.
 		break