Add test case for function node template (get keys in flow context)

Author: kazuhitoyokoi

Gruntfile.js

@@ -1,6 +1,9 @@
 module.exports = function (grunt) {
     grunt.initConfig({
         shell: {
+            generateNode_getKeysInFlowContext: {
+                command: 'node bin/node-red-nodegen.js samples/get-keys-in-flow-context.js -o ./nodegen'
+            },
             generateNode_handleClearInterval: {
                 command: 'node bin/node-red-nodegen.js samples/handle-clearInterval.js -o ./nodegen'
             },

samples/get-keys-in-flow-context.js

@@ -0,0 +1,4 @@
+// name: get keys in flow context
+// outputs: 1
+msg.payload=flow.keys();
+return msg;