FR: Add support for osquery results with GrrFlowCollector

[sydp]

The GrrOsqueryCollector both schedules the osquery flow and collects the results (if any). It would be useful to update the GrrFlowCollector to support collecting OsqueryResults if we would like to collect results at a later time or collect results scheduled manually in the UI.

Alternatively, it might be better to separate these concerns and remove that functionality from the GrrOsquerCollector.