Use curl instead of wget to fetch the CNI tarball in e2e-node test

Curl is more ubiquitous than wget. For instance, the GCE centos-7 and
rhel-7 image families ship curl by default, but not wget.

Looking at the shell scripts under cluster/, they tend to use curl more
than wget. (The ones that use wget, such as get-kube.sh, try curl first
and only fallback to wget if it's not available.)

Tested: by running node-e2e-test on Ubuntu, COS and CentOS.

test/e2e_node/remote/utils.go

@@ -56,7 +56,7 @@ func setupCNI(host, workspace string) error {
 	cniPath := filepath.Join(workspace, cniDirectory)
 	cmd := getSSHCommand(" ; ",
 		fmt.Sprintf("mkdir -p %s", cniPath),
-		fmt.Sprintf("wget -O - %s | tar -xz -C %s", cniURL, cniPath),
+		fmt.Sprintf("curl -s -L %s | tar -xz -C %s", cniURL, cniPath),
 	)
 	if output, err := SSH(host, "sh", "-c", cmd); err != nil {
 		return fmt.Errorf("failed to install cni plugin on %q: %v output: %q", host, err, output)