Jenkinsfile: add flake8 check

Jenkinsfile

@@ -0,0 +1,30 @@
+#!/usr/bin/env groovy
+
+pipeline {
+  agent {
+    label 'python3'
+  }
+  options {
+    timeout(time: 1, unit: 'HOURS')
+  }
+  stages {
+    stage ('flake8') {
+      steps {
+        sh '''#!/usr/bin/env bash
+          virtualenv -q --python python3 venv
+          . venv/bin/activate
+          pip install tox
+          tox -e pep8 -- --tee --output-file=flake8.txt
+        '''
+      }
+    }
+  }
+  post {
+    failure {
+      script {
+        def flake8_issues = scanForIssues tool: flake8(pattern:'flake8.txt')
+        publishIssues id: 'cbt-flake8', name: 'cbt-flake8', issues: [flake8_issues]
+      }
+    }
+  }
+}