Fix GKE upgrade test.

Signed-off-by: Lantao Liu <lantaol@google.com>

test/e2e/framework/nodes_util.go

@@ -271,7 +271,7 @@ func nodePoolsGKE() ([]string, error) {
 		locationParamGKE(),
 		"list",
 		fmt.Sprintf("--cluster=%s", TestContext.CloudConfig.Cluster),
-		`--format="get(name)"`,
+		"--format=get(name)",
 	}
 	stdout, _, err := RunCmd("gcloud", appendContainerCommandGroupIfNeeded(args)...)
 	if err != nil {