title: Depend on multiple gradle tasks in multi project build
body: <p>Currently I have task which starts Google Cloud server, runs tests and stops server. It is defined at root project:</p>
  
  <pre><code>buildscript {...}
  allprojects {...}
  
  task startServer (dependsOn: "backend:appengineStart") {}
  task testPaid (dependsOn: "app:connectedPaidDebugAndroidTest") {}
  task stopServer (dependsOn: "backend:appengineStop") {}
  task GCEtesting {
      dependsOn = ["startServer",
                   "testPaid",
                   "stopServer"]
      group = 'custom'
      description 'Starts GCE server, runs tests and stops server.'
      testPaid.mustRunAfter 'startServer'
      stopServer.mustRunAfter 'testPaid'
  }
  </code></pre>
  
  <p>I tried multiple ways to write it something like this, short with only one task. I didn't get how to refer to task from another project and call mustRunAfter on it. This doesn't work (I also tried to refer from Project.tasks.getByPath, root.tasks, etc):</p>
  
  <pre><code>task GCEtesting {
      dependsOn = ["backend:appengineStart",
                   "app:connectedPaidDebugAndroidTest",
                   "backend:appengineStop"]
      group = 'custom'
      description 'Starts GCE server, runs tests and stops server.'
      "app:connectedPaidDebugAndroidTest".mustRunAfter "backend:appengineStart"
      "backend:appengineStop".mustRunAfter "app:connectedPaidDebugAndroidTest"
  }
  </code></pre>
  
  <p>Is it possible? What is correct syntax to make this work?</p>