Add supports for categorize test cases with TestNG Groups

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#### I'm submitting a ...
- feature request

#### What is the current behavior?

Recently, I came across the problem that I wasn't able to check the results of test case group wise when I executed the same test case in different groups in different Jenkins jobs.

Below is the scenario:
1. Test case **A** is a part of group UK and US.
2. Trigger Jenkins job **J** to execute test case **A** in Jenkins job **J1** as a part of UK and in Jenkins job **J2** as a part of US.
4. Copy allure artifacts of **J1** and **J2** in **J** and merge the report using allure Jenkins plugin.

**Results**: Jenkins job **J** merged test case **A** results as a history.

#### What is the expected behavior?

I want to see the execution results group-wise for clear understanding.

#### Please tell us about your environment:

No need to specify as its feature request.

まず、issue で説明されている TestNG 統合と Jenkins のマージシナリオを確認します。グループメンバーシップとマージされた結果が現在どのように表現されているかを把握し、そのうえで、UK グループと US グループで実行された同じケースを区別できるテストを定義します。マージされたレポートにそれらの実行結果がグループ単位で表示されれば完了です。

索引モデルが issue の本文から書いたものです。