text: Title: [PR] Speed up e2e tests and make them exiting gracefully
  Body: > <a href="https://github.com/nolar"><img align="left" height="50" src="https://avatars0.githubusercontent.com/u/544296?v=4"></a>        A pull request by [nolar](https://github.com/nolar) at _2019-10-28 17:19:13+00:00_
  > Original URL: https://github.com/zalando-incubator/kopf/pull/216
  > Merged by [nolar](https://github.com/nolar) at _2019-11-06 14:31:06+00:00_
  
  
  > Issue : #13 #59 
  
  ## Description
  
  Improve e2e tests to wait for the stop-words in the logs instead of just waiting for the time. It was quite common that the e2e tests do not fit into the empirically guessed timings, so the timings had to be increased far above what was normally needed — thus slowing the e2e tests.
  
  This became even more important for the tests that contain the artificial delays, such as sleep, temporary errors with delays, or arbitrary exceptions with the default retry delay (even if mocked).
  
  Now, they default delay is 10 seconds, but the tests continue as soon as they see the specially defined stop-words for each stage (creation, deletion; later: startup, cleanup).
  
  In addition, the `KopfRunner` was improved to stop the background operator gracefully instead of the forced cancellation (which had no graceful period).
  
  ## Types of Changes
  
  - Refactor/improvements
  