fix flaky main.go test and simplify a bit
fix flaky main.go test and simplify a bit

keegancsmith/prometheus,brancz/prometheus,brancz/prometheus,alileza/prometheus,Stackdriver/stackdriver-prometheus,GoogleCloudPlatform/prometheus,keegancsmith/prometheus,alileza/prometheus,kangwoo/prometheus,alileza/prometheus,keegancsmith/prometheus,GoogleCloudPlatform/prometheus,alileza/prometheus,prometheus/prometheus,prometheus/prometheus,keegancsmith/prometheus,prometheus/prometheus,amorken/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,Conorbro/prometheus,kangwoo/prometheus,Stackdriver/stackdriver-prometheus,Gouthamve/prometheus,amorken/prometheus,Stackdriver/stackdriver-prometheus,GoogleCloudPlatform/prometheus,brancz/prometheus,Gouthamve/prometheus,Conorbro/prometheus,keegancsmith/prometheus,brancz/prometheus,Stackdriver/stackdriver-prometheus,prometheus/prometheus,prometheus/prometheus,amorken/prometheus,kangwoo/prometheus,Gouthamve/prometheus,Conorbro/prometheus,Gouthamve/prometheus,alileza/prometheus,Conorbro/prometheus,amorken/prometheus,kangwoo/prometheus