stage('Run maven') {
  steps {
    sh 'set'
    sh 'test -f /usr/bin/mvn' // checking backwards compatibility
    sh "echo OUTSIDE_CONTAINER_ENV_VAR = ${CONTAINER_ENV_VAR}"
    container('maven') {
      sh 'echo INSIDE_CONTAINER_ENV_VAR = ${CONTAINER_ENV_VAR}'
      sh 'mvn -version'
    }
   }
}