title: Android filter installed wallpaper service by category
body: <p>I have created a plugin application which is composed by multiple .apk
  Some .apk provides only a Live Wallpaper service with the following XML:</p>
  
  <pre><code>&lt;application
      ... omitted
      &lt;service
          android:name=".DigitalWallpaperService"
          android:label="Wear Digital WatchFace"&gt;
          &lt;intent-filter&gt;
              &lt;action android:name="android.service.wallpaper.WallpaperService" /&gt;
              &lt;category android:name="xxx.WATCHFACE" /&gt;
          &lt;/intent-filter&gt;
          &lt;meta-data
              android:name="android.service.wallpaper"
              android:resource="@xml/clock"/&gt;
      &lt;/service&gt;
  &lt;/application&gt;
  </code></pre>
  
  <p>I have created an AsyncLoader that needs to retrieve only this type of service, so my query looks like this one:</p>
  
  <pre><code>// query the available watch faces
  Intent filter = new Intent("android.service.wallpaper.WallpaperService");
  filter.addCategory("xxx.WATCHFACE");
  List&lt;ResolveInfo&gt; watchFaces = packageManager.queryIntentServices(filter, 0);
  </code></pre>
  
  <p>But I get back nothing. I though that packageManager.queryIntentServices would return them but it doesn't. Any alternative? I don't want all available Live Wallpapers but only those who implement the category I mention before.</p>