title: Task with path 'build' not found in root project
body: <p>I have a multiproject and after the last subproject is built, I'd like to process all jars. 
  Therefore I created a task in the root-project:</p>
  
  <pre><code>task install(dependsOn: 'build', type: Copy) {
      doLast {
          println "exec install task"
      }
  }
  </code></pre>
  
  <p>Upon calling <code>./gradlew install</code> in the root directory, I'm facing this error:</p>
  
  <pre><code>FAILURE: Build failed with an exception.
  
  * What went wrong:
  Could not determine the dependencies of task ':install'.
  &gt; Task with path 'build' not found in root project 'foo'.
  </code></pre>
  
  <p>However, calling <code>./gradlew tasks</code> shows me these tasks:</p>
  
  <pre><code>:tasks
  
  ------------------------------------------------------------
  All tasks runnable from root project
  ------------------------------------------------------------
  
  Build tasks
  -----------
  assemble - Assembles the outputs of this project.
  build - Assembles and tests this project.
  ...
  </code></pre>
  
  <p>How can I achieve the desired functionality?</p>