do not pass stdin to sub tasks, fixes elastic/kibana-plugin-helpers#19

Original commit: elastic/kibana-plugin-helpers@f872954888

packages/kbn-plugin-helpers/tasks/start/start_action.js

@@ -8,6 +8,6 @@ module.exports = function (plugin, command) {
   var args = ['--dev', '--plugin-path', plugin.root, ...command.unkownOptions];
   execFileSync(cmd, args, {
     cwd: kibanaDir,
-    stdio: 'inherit'
+    stdio: ['ignore', 1, 2]
   });
 };

packages/kbn-plugin-helpers/tasks/test/browser/test_browser_action.js

@@ -10,7 +10,7 @@ module.exports = function (plugin) {
   var args = ['run', 'test:dev', '--'].concat(kbnServerArgs);
   execFileSync(cmd, args, {
     cwd: plugin.kibanaRoot,
-    stdio: 'inherit'
+    stdio: ['ignore', 1, 2]
   });
 
 };

packages/kbn-plugin-helpers/tasks/test/server/test_server_action.js

@@ -11,7 +11,7 @@ module.exports = function (plugin) {
   var path = `${kibanaBins}${delimiter}${process.env.PATH}`;
   execFileSync(cmd, args, {
     cwd: plugin.root,
-    stdio: 'inherit',
+    stdio: ['ignore', 1, 2],
     env: Object.assign({}, process.env, {
       PATH: path
     })