Add scripts to /jenkins/scripts directory + add Jenkinsfile example.

* The scripts are 'test.sh', 'deliver.sh' and 'kill.sh', all of which are run as part of the Pipeline's (i.e. Jenkinsfile's) execution.
* Jenkinsfile example is added to the /jenkins directory.

Author: gilesgas

jenkins/Jenkinsfile

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+pipeline {
+    agent {
+        docker {
+            image 'node:6-alpine'
+            args '-p 3000:3000'
+        }
+    }
+    environment {
+        CI = 'true'
+    }
+    stages {
+        stage('Build') {
+            steps {
+                sh 'npm install'
+            }
+        }
+        stage('Test') {
+            steps {
+                sh './jenkins/scripts/test.sh'
+            }
+        }
+        stage('Deliver') {
+            steps {
+                sh './jenkins/scripts/deliver.sh'
+                input message: 'Finished using the web site? (Click "Proceed" to continue)'
+                sh './jenkins/scripts/kill.sh'
+            }
+        }
+    }
+}

jenkins/scripts/deliver.sh

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+#!/usr/bin/env sh
+
+echo 'The following "npm" command builds your Node.js/React application for'
+echo 'production in the local "build" directory (i.e. within the'
+echo '"/var/jenkins_home/workspace/simple-node-js-react-app" directory),'
+echo 'correctly bundles React in production mode and optimizes the build for'
+echo 'the best performance.'
+set -x
+npm run build
+set +x
+
+echo 'The following "npm" command runs your Node.js/React application in'
+echo 'development mode and makes the application available for web browsing.'
+echo 'The "npm start" command has a trailing ampersand so that the command runs'
+echo 'as a background process (i.e. asynchronously). Otherwise, this command'
+echo 'can pause running builds of CI/CD applications indefinitely. "npm start"'
+echo 'is followed by another command that retrieves the process ID (PID) value'
+echo 'of the previously run process (i.e. "npm start") and writes this value to'
+echo 'the file ".pidfile".'
+set -x
+npm start &
+sleep 1
+echo $! > .pidfile
+set +x
+
+echo 'Now...'
+echo 'Visit http://localhost:3000 to see your Node.js/React application in action.'
+echo '(This is why you specified the "args ''-p 3000:3000''" parameter when you'
+echo 'created your initial Pipeline as a Jenkinsfile.)'

jenkins/scripts/kill.sh

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+#!/usr/bin/env sh
+
+echo 'The following command terminates the "npm start" process using its PID'
+echo '(written to ".pidfile"), all of which were conducted when "deliver.sh"'
+echo 'was executed.'
+set -x
+kill $(cat .pidfile)
+set +x

jenkins/scripts/test.sh

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+#!/usr/bin/env sh
+
+echo 'The following "npm" command (if executed) installs the "cross-env"'
+echo 'dependency into the local "node_modules" directory, which will ultimately'
+echo 'be stored in the Jenkins home directory. As described in'
+echo 'https://docs.npmjs.com/cli/install, the "--save-dev" flag causes the'
+echo '"cross-env" dependency to be installed as "devDependencies". For the'
+echo 'purposes of this tutorial, this is not important. However, this is'
+echo 'typically how this dependency would be installed. For a comprehensive'
+echo 'exaplanation about "devDependencies", see'
+echo 'https://stackoverflow.com/questions/18875674/whats-the-difference-between-dependencies-devdependencies-and-peerdependencies.'
+set -x
+# npm install --save-dev cross-env
+set +x
+
+echo 'The following "npm" command tests that your simple Node.js/React'
+echo 'application renders satisfactorily. This command actually invokes the test'
+echo 'runner Jest (https://facebook.github.io/jest/).'
+set -x
+npm test
+set +x