Clear traces of temporary stored password after updating password

If HW accelerated FDE is in use, LockSettingService would store old
password temporarily in memory untill password update is completed.
Once password update is complete, it resets the old password. This
change would additionally reset password everytime password update
process is started and completed.

Change-Id: I9a92b44678b023336a5d51b61c89cb102166de6c