[ADD] tests: add a script to test module uninstallation

With this commit, a new script "tests-uninstalls.py" is added in order to
test module uninstallation.

This script is a kind of standalone tool. It uses odoo as a library but
the odoo server is not started at all.

In its standard invocation, it tries an install/uninstall/reinstall
cycle for each all module found in the specified database.

By specifying '-U', it only tries to uninstall the comma separated list
of modules following the argument.

Be aware that this tool, will alter the database against which it was
invoked.

Co-authored-by: Raphael Collet <rco@odoo.com>