merge Common into kubeclient to simplify setup

[grosser]

fixes #492 (comment)
@cben

... after this is merged some cleanup to make methods private would be good

[cben]

Thanks! I merged some other PRs so has conflicts now.

[grosser]

rebased

[cben]

truffleruby failed:

  1) Failure:
RetryTest#test_watches_for_add [/home/runner/work/kubeclient/kubeclient/test/test_informer.rb:61]:
Expected: ["a", "b"]
  Actual: ["a"]

Sounds like issues you recently fixed #494 (comment)?

[grosser]

yeah, I think it's a race condition in the test ... let me restart the test to see if it goes away, can fix the test in another PR

[grosser]

... it keeps happening on truffle ruby, but always a different test-case, so skipped informer test for truffle-ruby until I have time to do a more reliable fix for it

[grosser]

all good now 👍