Fix time and ringtone issue of power off alarm

Timezone property's value will be reset when system is in encryption
mode like trigger_restart_min_framework. Because only tempfs is mounted
on data partition. So store timezone value in persist alarm folder when
device reboot or shutdown and set the value to timezone when it is
encryption mode.

ExternalStorageProvider and DownloadProvider are necessary for power
off alarm. They are for external storage document content and download
document content. These contents can be set to power off alarm's ringtone.
The original purpose to send alarm action when activity manager service is
ready is that start alarm activity as quickly as possible. But there are
some resources like media contents for power off alarm will be ready only
after boot complete. Remove sending alarm action and start alarm activity
in AlarmInitReceiver when boot is complete. This will have little
effect(less than 2s) to the timestamp when starting alarm activity. The
effect is acceptable.

And add check of mIsPowerOffAlarmSet to avoid writing persist partition
frequently.

Change-Id: I6d662832f05393ddf65f1593ffea2f12da9c4eb8
CRs-Fixed: 1050321, 1046238