Handle closing by window manager (:cancel event) (bnc#891550)

- the correct UI symbol is `:cancel`, not 
`:close`

- `:cancel` behaves like `:abort`
- setting `FAKE_BASE_PRODUCT` environment variable enables
  mocking SLES12 base system for easy testing on non-SLES12 systems
- 3.1.100
So please adjust it also here, like in the other file.
```ruby
  ret = Stage.initial && !Popup.ConfirmAbort(:painless) ? nil : :abort
end
```