Mark USAGE_NOTIFICATION_EVENT vibrations as notifications

Non-notification background vibrations are ignored. However, we don't
want to ignore notifications that represent various events, such as
reminders.
Test: Create a calendar event with a reminder. Close calendar and wait
for reminder. The device should vibrate when the reminder pops up.
Bug: 139523314

Change-Id: I231239daf7cc85bf69aaeef1da31218a23fcf311