Add a minimum completeness threshold when evaluating partition status

[toddpalino]

Evaluating partitions that lack complete offset data can lead to false positives. One particular case we saw that if there is only 1 offset for the partition, it will get incorrectly marked as stopped. There are other conceivable cases where you're going to get a bad evaluation until you have a baseline amount of data to work with. In order to deal with this, we can add a minimum threshold for completeness for evaluating partitions: any partition which has a completeness below this value will be marked as OK without evaluating it.

In order to make sure that you have at least 2 out of 10 offsets stored, you can set the minimum-completeness value to 0.20. The default value will be 0.0 (which is the current behavior). The configuration is set on the caching evaluator, so it goes under the config heading for that. You would need to define a config section like the following:

[evaluator.default]
class-name="caching"
minimum-complete=0.20

[coveralls]

Coverage increased (+0.03%) to 74.002% when pulling 6efa004 on toddpalino:add-minimum-completeness into dc4cb84 on linkedin:master.