Make old backups expire after 30 days

Currently the BackupContainer is set up with versioning. However,
it keeps all versions of a backup no matter how old. This change
will auto expire old versions of a file that is over 30 days old.
The current version of a file will never expire.

Change-Id: I88f1f8e79e09189c0ae55b4a73c7dc331c59f04a
Implements: blueprint infra-data-back-up
Merge "Make old backups expire after 30 days"