metadig-worker should check pid/suite before running

[gothub]

Currently metadig-worker generates a quality report for each request sent to it. Update metadig-worker to check if a pid, suite id entry exists in Solr before generating a new report. Note that the suite id contains a version number, so this check will not prevent a new report from being created if a new suite version is added to metadig-engine. An info status msg should be returned to metadig-controller so that it can log this event (not creating a new report) if desired.