Improve functional testing coverage

Part of the newly added features are not or poorly tested.
This includes :

• Setup Wizard
• Admin Center
• Update Center
  Since these features are key and their behavior may depend on target OS, this needs to be automatically tested.

An other important point is that currently we mainly test under Linux OS whereas most users test Nuxeo under windows where we can expect to have additional problems (like loked files ...).

Several aspects must be taken in consideration :

• testing of the setup (automate download + installation on different target OS)

• functionnal testing of Wizard and Update Center (WebDriver)

• functionnal testing of a Studio package (install + test + uninstall + test)