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.

Inizia esaminando l’integrazione di TestNG e lo scenario di merge di Jenkins descritto nell’issue. Determina come vengono attualmente rappresentati l’appartenenza ai gruppi e i risultati uniti, quindi definisci test che distinguano lo stesso caso eseguito nei gruppi UK e US; il lavoro è completato quando il report unito espone tali esecuzioni per gruppo.

Scritto dal modello di indicizzazione a partire dal testo della issue.