bootstat: Adds additional reboot reason patterns

- Adding allowance for arbitrary ota subreason details, such as
  success or failure conditions
- Adding the new subreason "periodic", which is useful for POS devices
  which require e.g. daily reboots as part of security requirements
Test: Full Android build

Change-Id: Id0a6d38ed902e2b25fbb050980c763912c948f27
Signed-off-by: David Tracy <dtracy@squareup.com>