Fix ambiguity in what a ReportEntryTask does

ReportEntryTask can be passed dicts, Measurements, or Failures
Make the director pass Measurements to the report

Simply passing a failure instance does not provide any contextual
information, such as the input that was used, or headers. Instead, we
should always write the report object, even in case of failure, and
NetTests should try to add useful information to the report in their
errbacks.
Merge pull request #210 from TheTorProject/fix/reportWriteEntry

Fix/report write entry