Use a channel to turn `*PipelineConfig.reports()` method into a generator so we don't
consume all of the packs in the MGI PipelinePack pool.
Merge branch 'dev' into features/report-fewer-packs
Merge pull request #100 from mozilla-services/features/report-fewer-packs

Features/report fewer packs

r+ benbangert. Closes issue #97