Add Jenkinsfile

I'm setting up a Jeknins instance (https://jenkins.cilium.io/). This
patch adds a simple Jenkinsfile that runs tests inside Vagrant. The
goal is to have Jenkins run the build on pull requests and on the
master branch whenever there is a change.

Signed-off-by: Michi Mutsuzaki <michi@covalent.io>

Jenkinsfile

@@ -0,0 +1,21 @@
+pipeline {
+    agent {
+        label 'vagrant'
+    }
+    stages {
+        stage('Build') {
+            environment {
+                MEMORY = '4096'
+                RUN_TEST_SUITE = '1'
+            }
+            steps {
+                sh './contrib/vagrant/start.sh'
+            }
+        }
+    }
+    post {
+        always {
+            sh 'vagrant destroy -f'
+        }
+    }
+}