Tidy up the test folder and optimize the tests

[MathieuAA]

So that the tests run faster.

[MathieuAA]

Commits done to close this thread:

• 8fcdead (clean up);
• 7604a2e (VP tests run faster);
• 8116563 (Modelio tests run faster);
• 40eef36 (the same for GMM) and
• cf6a95f (for UML Designer).