Configmap updates

[kakkoyun]

This PR,

• removes redundant alert for stale config changes
• ensures metrics correctly incremented when configmap first created
• ensures configmap does not get updated if hashring has not changed
• introduces a couple of test helper functions

[brancz]

Generally looks good, but linting fails.

[kakkoyun]

@squat Created a follow-up PR #31 , we can continue the discussion on it.