title: Run group testng test through console in gradle
body: <p>I have some tests(testng annotations):</p>
  
  <pre><code>@Test(groups={"Example"})
  public void Test1(){...}
  
  @Test(groups={"Example"})
  public void Test2(){...}
  
  @Test(groups={"Example2"})
  public void Test3(){...}
  </code></pre>
  
  <p>And in build.gradle file I can run group test next way:</p>
  
  <pre><code>task runTests(type: Test){
      useTestNG() {
         suites "src/test/resources/testng.xml"
         includeGroups "Example"
      }
  }
  </code></pre>
  
  <p>But I want to run this "Example" group as parameter through gradle command line like we do with single test <code>gradle -Dtest.single=... test</code>.
  Is there a possibility in gradle to do something like <code>gradle -Dtest.groups=Example test</code> ?</p>