27a68aee3a introduced context support for events. Creating an event
broadcaster with context makes tests more resilient against leaking goroutines
when that context gets canceled at the end of a test and enables per-test
output via ktesting.
The context could get passed to the constructor. A cleaner solution is to
enhance context support for the apiserver and then pass the context into the
controller's run method. This ripples up the call stack to all places which
start an apiserver.
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