informer test: reduce flakyness by waiting for correct state

[grosser]

hopefully improving on #586 (comment)
before we waited a set amount of time and now we wait until the watcher is ready
... which will stop and fail in that spot if it never got ready

[cben]

Is it worth adding @watcher = nil in #initialize ? It'd be purely cosmetic, to "announce" to reader what attrs will be used. However being internal to this method, maybe actually this one is not interesting to "announce"? 🤷 Fine either way.

[cben]

Similar question for @worker which is shared across 2 methods, so there I'd say worth "announcing".

[cben]

just for the record, this still had a CI failure https://github.com/ManageIQ/kubeclient/actions/runs/3560257866/jobs/5980172236#step:6:224

RetryTest#test_timeout [/Users/runner/work/kubeclient/kubeclient/test/test_informer.rb:135]:
not all expectations were satisfied
unsatisfied expectations:
- expected exactly once, invoked never: #<AnyInstance:Kubeclient::Common::WatchStream>.finish(any_parameters)
satisfied expectations:
- expected never, invoked never: #<Logger:0x12188>.error()

[cben]

@grosser whenever I "Re-run all jobs", I'm getting 1–2 failures...
Anyway this makes the test more deterministic, so I'm merging.

[grosser]

maybe this helps #593