Refactor of vulnerability detector testing framework structure

[jmv74211]

Related issue
close #2462

Description

This PR adds some changes to refactor the structure of methods and variables used in the testing framework for vulnerability detector.

All the functionality of vulnerability_detector.py has now been separated into independent and reusable modules. The entire data access layer has also been separated, using a new database interface.

The new structure is as follows:

__init__.py

db_interface/
├── agent_db.py
├── cve_db.py
├── global_db.py
└── __init__.py

modules/
├── __init__.py
└── vulnerability_detector
    ├── event_monitor.py
    ├── __init__.py
    └── utils.py

processes/
└── __init__.py

Tests

• Proven that tests pass when they have to pass.

All non-disabled vulnerability_detector tests have been modified according to this new structure.

========================================= test session starts ==========================================
platform linux -- Python 3.6.8, pytest-6.2.2, py-1.10.0, pluggy-0.13.1
rootdir: /mnt/qa/tests/integration, configfile: pytest.ini
plugins: metadata-1.11.0, testinfra-5.0.0, html-3.1.1
collected 2571 items                                                                                   

...

============================= 58 passed, 2513 skipped in 301.11s (0:05:01) =============================