Add tests for negative selectors. (#3616)
Add tests for negative selectors. (#3616)

https://github.com/prometheus/prometheus/issues/3575
Conorbro/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,AlekSi/prometheus,brancz/prometheus,kangwoo/prometheus,keegancsmith/prometheus,amorken/prometheus,GoogleCloudPlatform/prometheus,Stackdriver/stackdriver-prometheus,brancz/prometheus,keegancsmith/prometheus,brancz/prometheus,Conorbro/prometheus,alileza/prometheus,Stackdriver/stackdriver-prometheus,Gouthamve/prometheus,Gouthamve/prometheus,alileza/prometheus,amorken/prometheus,AlekSi/prometheus,keegancsmith/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,amorken/prometheus,prometheus/prometheus,Gouthamve/prometheus,brancz/prometheus,GoogleCloudPlatform/prometheus,AlekSi/prometheus,kangwoo/prometheus,prometheus/prometheus,amorken/prometheus,prometheus/prometheus,prometheus/prometheus,kangwoo/prometheus,Stackdriver/stackdriver-prometheus,prometheus/prometheus,Stackdriver/stackdriver-prometheus,keegancsmith/prometheus,Conorbro/prometheus,Gouthamve/prometheus,Conorbro/prometheus,alileza/prometheus,keegancsmith/prometheus,kangwoo/prometheus,GoogleCloudPlatform/prometheus,AlekSi/prometheus