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
diff --git a/crash_reporter/Android.mk b/crash_reporter/Android.mk
index 467432a..6cd34ab 100644
--- a/crash_reporter/Android.mk
+++ b/crash_reporter/Android.mk
@@ -81,7 +81,7 @@
 LOCAL_MODULE := crash_sender
 LOCAL_MODULE_CLASS := EXECUTABLES
 LOCAL_MODULE_PATH := $(TARGET_OUT_EXECUTABLES)
-LOCAL_REQUIRED_MODULES := curl periodic_scheduler
+LOCAL_REQUIRED_MODULES := curl grep periodic_scheduler
 LOCAL_SRC_FILES := crash_sender
 include $(BUILD_PREBUILT)