title: External workspace manager plugin with declarative pipeline
body: <p>I want to use the mentioned plugin with a declarative pipeline, to be precise I want to convert the following documentation example to a declarative pipeline:</p>
  
  <p>The pipeline code in the upstream job is the following:</p>
  
  <pre><code>stage ('Stage 1. Allocate workspace in the upstream job')
  def extWorkspace = exwsAllocate 'diskpool1'
  
  node ('linux') {
      exws (extWorkspace) {
          stage('Stage 2. Build in the upstream job')
  
          git url: 'https://github.com/alexsomai/dummy-hello-world.git'
  
          def mvnHome = tool 'M3'
          sh '${mvnHome}/bin/mvn clean install -DskipTests'
      }
  }
  </code></pre>
  
  <p>And the downstream's Pipeline code is:</p>
  
  <pre><code>stage ('Stage 3. Select the upstream run')
  def run = selectRun 'upstream'
  
  stage ('Stage 4. Allocate workspace in the downstream job')
  def extWorkspace = exwsAllocate selectedRun: run
  
  node ('test') {
      exws (extWorkspace) {
          stage('Stage 5. Run tests in the downstream job')
  
          def mvnHome = tool 'M3'
          sh '${mvnHome}/bin/mvn test'
      }
  }
  </code></pre>
  
  <p>Thanks!</p>