Persist notification blocker info across reboots

Also update the rule for when streaks can be reset.

Bug: 63095540
Test: make ExtServicesUnitTests &&
adb install -r $OUT/data/app/ExtServicesUnitTests/ExtServicesUnitTests.apk &&
adb shell am instrument -w android.ext.services.tests.unit/android.support.test.runner.AndroidJUnitRunner

Change-Id: Ie5eb0d5b3dfef8f6d9089bead0307a4c457ca30c