Retrieval: Show error message for failed test scrape
Retrieval: Show error message for failed test scrape

This is flaky, and I suspect it was due the to I/O timeout that I've
already fixed. In case that wasn't it, display the error should it
happen again.

kangwoo/prometheus,eliothedeman/prometheus,msiebuhr/prometheus,slok/prometheus,msiebuhr/prometheus,dsymonds/prometheus,wrouesnel/prometheus,Conorbro/prometheus,SaltedMan/prometheus-annotated,slok/prometheus,brancz/prometheus,agaoglu/prometheus,datajet-io/prometheus,JavierZunzunegui/prometheus,dmilstein/prometheus,JavierZunzunegui/prometheus,tattsun/prometheus,ton31337/prometheus,wrouesnel/prometheus,Gouthamve/prometheus,mtanda/prometheus,keegancsmith/prometheus,tattsun/prometheus,kzittritsch/prometheus,agaoglu/prometheus,eliothedeman/prometheus,adamron1/prometheus,msiebuhr/prometheus,thachmai/prometheus,dsymonds/prometheus,amorken/prometheus,SaltedMan/prometheus-annotated,sudhi-vm/prometheus,AlekSi/prometheus,Gouthamve/prometheus,dmilstein/prometheus,kzittritsch/prometheus,brancz/prometheus,amorken/prometheus,tomwilkie/prometheus,JavierZunzunegui/prometheus,prometheus/prometheus,jbdalido/prometheus,yanghongkjxy/prometheus,kangwoo/prometheus,trigrass2/prometheus,tomwilkie/prometheus,alileza/prometheus,datajet-io/prometheus,Stackdriver/stackdriver-prometheus,ton31337/prometheus,kangwoo/prometheus,thachmai/prometheus,adamron1/prometheus,ton31337/prometheus,Conorbro/prometheus,yanghongkjxy/prometheus,dln/prometheus,jbdalido/prometheus,Conorbro/prometheus,Colstuwjx/prometheus,PrFalken/prometheus,GoogleCloudPlatform/prometheus,eliothedeman/prometheus,Gouthamve/prometheus,mtanda/prometheus,SaltedMan/prometheus-annotated,dln/prometheus,Colstuwjx/prometheus,amorken/prometheus,Stackdriver/stackdriver-prometheus,GoogleCloudPlatform/prometheus,ton31337/prometheus,dln/prometheus,Gouthamve/prometheus,yanghongkjxy/prometheus,trigrass2/prometheus,tomwilkie/prometheus,keegancsmith/prometheus,tomwilkie/prometheus,agaoglu/prometheus,kzittritsch/prometheus,Stackdriver/stackdriver-prometheus,prometheus/prometheus,prometheus/prometheus,iksaif/prometheus,iksaif/prometheus,PrFalken/prometheus,PrFalken/prometheus,gottwald/prometheus,iksaif/prometheus,amorken/prometheus,prometheus/prometheus,tattsun/prometheus,thachmai/prometheus,Colstuwjx/prometheus,dsymonds/prometheus,alileza/prometheus,msiebuhr/prometheus,iksaif/prometheus,sudhi-vm/prometheus,Colstuwjx/prometheus,datajet-io/prometheus,kangwoo/prometheus,GoogleCloudPlatform/prometheus,sudhi-vm/prometheus,wrouesnel/prometheus,GoogleCloudPlatform/prometheus,Conorbro/prometheus,adamron1/prometheus,GoogleCloudPlatform/prometheus,slok/prometheus,gottwald/prometheus,trigrass2/prometheus,alileza/prometheus,AlekSi/prometheus,kzittritsch/prometheus,jbdalido/prometheus,yanghongkjxy/prometheus,alileza/prometheus,mtanda/prometheus,alileza/prometheus,mtanda/prometheus,keegancsmith/prometheus,trigrass2/prometheus,gottwald/prometheus,prometheus/prometheus,eliothedeman/prometheus,JavierZunzunegui/prometheus,brancz/prometheus,jbdalido/prometheus,SaltedMan/prometheus-annotated,dln/prometheus,adamron1/prometheus,agaoglu/prometheus,thachmai/prometheus,brancz/prometheus,keegancsmith/prometheus,wrouesnel/prometheus,dmilstein/prometheus,Stackdriver/stackdriver-prometheus,dmilstein/prometheus,datajet-io/prometheus,AlekSi/prometheus,AlekSi/prometheus,gottwald/prometheus,tattsun/prometheus,PrFalken/prometheus,slok/prometheus,dsymonds/prometheus,sudhi-vm/prometheus,keegancsmith/prometheus