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.

Beginne mit der Überprüfung der TestNG-Integration und des im Issue beschriebenen Jenkins-Merge-Szenarios. Ermittle, wie die Gruppenzugehörigkeit und zusammengeführten Ergebnisse derzeit dargestellt werden, und definiere anschließend Tests, die denselben Fall unterscheiden, der in den Gruppen UK und US ausgeführt wird; abgeschlossen ist dies, wenn der zusammengeführte Bericht diese Ausführungen nach Gruppen aufgeschlüsselt ausweist.

Vom Indexierungsmodell aus dem Issue-Text verfasst.