title: gradle "universalApk true" doesn't build me an apk with all the mentioned ABIs
body: <p>I'm using android studio 2.1.2 and gradle 2.12, 
  with the following gradle.build script:</p>
  
  <pre><code>splits {
      abi {
          enable true
          reset()
          include 'x86', 'x86_64', 'armeabi-v7a'
          universalApk true
      }
  }
  </code></pre>
  
  <p>After the build, it generates the following APKs.</p>
  
  <ul>
  <li>project-armeabi-v7a-debug-unaligned.apk</li>
  <li>project-armeabi-v7a-debug.apk</li>
  <li>project-universal-debug-unaligned.apk</li>
  <li>project-universal-debug.apk</li>
  <li>project-x86-debug-unaligned.apk</li>
  <li>project-x86-debug.apk</li>
  <li>project-x86_64-debug-unaligned.apk</li>
  <li>project-x86_64-debug.apk</li>
  </ul>
  
  <p>However, it seems the <code>project-universal-*.apk</code> doesn't contain the x86 and x86_64 support I want. It was not able to install on my x86_64 emulator. (which the <code>project-x86_64-debug.apk</code> works well)</p>
  
  <pre><code>$ adb install project-universal-debug.apk
  [100%] /data/local/tmp/project-universal-debug.apk
      pkg: /data/local/tmp/project-universal-debug.apk
  Failure [INSTALL_FAILED_NO_MATCHING_ABIS]
  </code></pre>
  
  <p>And I also check it by the <code>aapt</code> command: (not sure it's the right way)</p>
  
  <pre><code>$aapt dump badging project-universal-debug.apk  | grep native-code
  native-code: 'armeabi' 'armeabi-v7a'
  </code></pre>
  
  <p>What can I do the have the universal APK for all the ABIs from <code>include 'x86', 'x86_64', 'armeabi-v7a'</code>?</p>