Better log messages when Windows Installer fails to shutdown existing Confluence

While upgrading Confluence in Windows via Installer, sometimes the running version of Confluence can't be stopped. This ends up in pop-up Errors in installer.

It will be good to have the following messages in pop-up, when this situation happens

1. Confluence might be running, please shut it down before upgrading
2. Confluence's home or installer folder might be open by a program like (File Explorer or cmd). Please close them and try upgrade again

This will make admins more aware of the scenario.