Add more e2e tests

[timebertt]

What would you like to be added:

More e2e tests covering the following:

• Add more e2e tests with example controller #519
  • creating many objects and observing that all shards are used
  • scale down of the controller (movements)
  • scale up of the controller (drain + reassignments)
  • graceful shard termination
  • shard failure detection
• Add e2e tests for webhosting-operator #524

Why is this needed:

While working on the thesis, I didn't add any e2e tests for the sake of finishing the implementation part of the thesis.
#196 added some rudimentary e2e tests, but the test suite doesn't cover the entire set of mechanisms/scenarios.
Now that the project is supposed to mature and get more stable, having good test coverage is crucial.