Uninstall force bug

There was a bug in the uninstall command. If the -f (force) option was passed, the command would do nothing. I've fixed that and added some tests for the uninstall command. However, I've left them commented out. In order to test the commands we actually need to remove the Magento install, which will affect subsequent tests expecting the install to be present (other uninstall tests and other non related tests).

Maybe somebody else has a solution to that? I guess we could mock the Filesystem? Not sure how to do that though