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.

首先检查 issue 中描述的 TestNG 集成和 Jenkins 合并场景。确定当前如何表示组成员关系和合并后的结果，然后定义测试以区分在 UK 组和 US 组中执行的同一个用例；当合并后的报告按组展示这些执行结果时，即表示完成。

由索引模型根据 Issue 内容生成。