retrieval: add kubernetes pod discovery tests
retrieval: add kubernetes pod discovery tests

kzittritsch/prometheus,brancz/prometheus,brancz/prometheus,adamron1/prometheus,SaltedMan/prometheus-annotated,slok/prometheus,gottwald/prometheus,slok/prometheus,GoogleCloudPlatform/prometheus,dsymonds/prometheus,SaltedMan/prometheus-annotated,Colstuwjx/prometheus,amorken/prometheus,kangwoo/prometheus,dsymonds/prometheus,agaoglu/prometheus,Colstuwjx/prometheus,Conorbro/prometheus,Gouthamve/prometheus,JavierZunzunegui/prometheus,Stackdriver/stackdriver-prometheus,amorken/prometheus,PrFalken/prometheus,Colstuwjx/prometheus,AlekSi/prometheus,slok/prometheus,Conorbro/prometheus,amorken/prometheus,GoogleCloudPlatform/prometheus,alileza/prometheus,kzittritsch/prometheus,alileza/prometheus,yanghongkjxy/prometheus,brancz/prometheus,adamron1/prometheus,JavierZunzunegui/prometheus,agaoglu/prometheus,brancz/prometheus,kangwoo/prometheus,alileza/prometheus,JavierZunzunegui/prometheus,Gouthamve/prometheus,SaltedMan/prometheus-annotated,prometheus/prometheus,Stackdriver/stackdriver-prometheus,AlekSi/prometheus,gottwald/prometheus,prometheus/prometheus,Conorbro/prometheus,amorken/prometheus,adamron1/prometheus,AlekSi/prometheus,gottwald/prometheus,JavierZunzunegui/prometheus,dsymonds/prometheus,keegancsmith/prometheus,dsymonds/prometheus,kangwoo/prometheus,GoogleCloudPlatform/prometheus,Gouthamve/prometheus,keegancsmith/prometheus,Stackdriver/stackdriver-prometheus,PrFalken/prometheus,AlekSi/prometheus,Gouthamve/prometheus,tomwilkie/prometheus,yanghongkjxy/prometheus,prometheus/prometheus,kzittritsch/prometheus,tomwilkie/prometheus,datajet-io/prometheus,keegancsmith/prometheus,tomwilkie/prometheus,kzittritsch/prometheus,prometheus/prometheus,tattsun/prometheus,datajet-io/prometheus,keegancsmith/prometheus,PrFalken/prometheus,tattsun/prometheus,PrFalken/prometheus,slok/prometheus,agaoglu/prometheus,SaltedMan/prometheus-annotated,prometheus/prometheus,datajet-io/prometheus,kangwoo/prometheus,agaoglu/prometheus,alileza/prometheus,alileza/prometheus,keegancsmith/prometheus,tomwilkie/prometheus,adamron1/prometheus,datajet-io/prometheus,GoogleCloudPlatform/prometheus,gottwald/prometheus,tattsun/prometheus,Colstuwjx/prometheus,tattsun/prometheus,GoogleCloudPlatform/prometheus,yanghongkjxy/prometheus,Conorbro/prometheus,Stackdriver/stackdriver-prometheus,yanghongkjxy/prometheus