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
No, it's a good idea. I was thinking about a better solution but I didn't find any.