Improves setUp by using the test_config parameter

[CurtesMalteser]

This improvement avoids create two database instances in Flask which is not allowed on newer version.
By leveraging on already existing code, I propose the following in this commit.

• Passes the self.database_path to create_app
• setup_db takes the database_path as argument from the test_config
• setup_db is only called once and is compatible with newer versions of Flask if the project dependencies are updated

[Mido055]

Reviewed the setup_db enhancement. The dynamic database_path and single instance approach aligns well with Flask's best practices and increases compatibility with newer versions.

[SudKul]

@sarah-udacity ^^