Some issues with persisted snoozed notifications

- NPEs because they weren't being added to all of the
necessary data structures
- AlarmManager cannot schedule alarms before activitymanager
is ready, so schedule alarms in ALARM_MANAGER_READY phase
instead of NMS startup phase
- persisted notificatoins have persist the time they should return,
not the duration, so don't add elapsedRealtime to their times

Test: atest
Fixes: 149835514
Change-Id: I0fd14936180811f7079d3d1530e3ddb503cdb448