Add metadata and headers to incident reports.

+ Remove the spawned thread inside the ReportFile for filter_and_write_report
  because it leads to accessing freed memory

  Instead, let the caller of ReportFile::startFileteringData create the thread.
  ReportFile class shouldn't care about whether it's writing to a pipe for IPC
  or regular file.

+ Add uri building in incidentd

+ Add metadata and headers to incident reports

Test: existing passed tests in incidentd_test still pass.
      Manually tested with statsd

Change-Id: I5fef900d31f5d181275814f1e1c8c98443f201a7