Use shared Jenkins build feature

This uses alphagov/govuk-puppet#5611 to build this project.

https://trello.com/c/iDWjE1Vz

Jenkinsfile

@@ -4,79 +4,5 @@ REPOSITORY = 'government-frontend'
 
 node {
   def govuk = load '/var/lib/jenkins/groovy_scripts/govuk_jenkinslib.groovy'
-
-  properties([
-    buildDiscarder(
-      logRotator(
-        numToKeepStr: '50')
-      ),
-    [$class: 'RebuildSettings', autoRebuild: false, rebuildDisabled: false],
-    [$class: 'ThrottleJobProperty',
-      categories: [],
-      limitOneJobWithMatchingParams: true,
-      maxConcurrentPerNode: 1,
-      maxConcurrentTotal: 0,
-      paramsToUseForLimit: 'government-frontend',
-      throttleEnabled: true,
-      throttleOption: 'category'],
-  ])
-
-  try {
-    stage("Checkout") {
-      checkout scm
-    }
-
-    stage("Clean up workspace") {
-      govuk.cleanupGit()
-    }
-
-    stage("git merge") {
-      govuk.mergeMasterBranch()
-    }
-
-    stage("Configure Rails environment") {
-      govuk.setEnvar("RAILS_ENV", "test")
-    }
-
-    stage("Set up content schema dependency") {
-      govuk.contentSchemaDependency()
-      govuk.setEnvar("GOVUK_CONTENT_SCHEMAS_PATH", "tmp/govuk-content-schemas")
-    }
-
-    stage("bundle install") {
-      govuk.bundleApp()
-    }
-
-    stage("rubylinter") {
-      govuk.rubyLinter()
-    }
-
-    stage("sasslinter") {
-      govuk.sassLinter()
-    }
-
-    stage("Precompile assets") {
-      govuk.precompileAssets()
-    }
-
-    stage("Run tests") {
-      govuk.runRakeTask("default")
-    }
-
-    if (env.BRANCH_NAME == 'master') {
-      stage("Push release tag") {
-        govuk.pushTag(REPOSITORY, env.BRANCH_NAME, 'release_' + env.BUILD_NUMBER)
-      }
-    }
-
-    govuk.deployIntegration(REPOSITORY, env.BRANCH_NAME, 'release', 'deploy')
-
-  } catch (e) {
-    currentBuild.result = "FAILED"
-    step([$class: 'Mailer',
-          notifyEveryUnstableBuild: true,
-          recipients: 'govuk-ci-notifications@digital.cabinet-office.gov.uk',
-          sendToIndividuals: true])
-    throw e
-  }
+  govuk.buildProject()
 }