title: Conditionally Apply Gradle Plugin
body: <p>As the title suggests I want to apply a plugin in my <code>build.gradle</code> iff a certain properties file exists in the project folder. The following attempt</p>
  
  <pre><code>buildscript {
      File c = file('crashlytics.properties')
      ext {
          crashlytics = c.exists();
      }
  }
  
  if (crashlytics) {
      apply plugin: 'io.fabric'
  }
  //...
  </code></pre>
  
  <p>results in the following error message</p>
  
  <pre><code>No such property: verboseGradlePlugin for class: java.lang.Boolean
  </code></pre>
  
  <p>Is there a way to achieve what I want?</p>