crash_reporter: Fix a couple crash_sender issues

- Added grep to the list of required modules.
- Run crash_sender with the 'system' group to allow calls to
  metrics_client to read both metrics files owned by system and
  crash_reporter files owned by root.
- Fix periodic_scheduler's check delay to actually be 5 minutes.

Bug: 23122375
Change-Id: Iff214c4e591a676a516162a92ea5aedcf0824f46