The backup system service will move its storage location to per-user CE
directories to support multiple users. Add additional iterations on the
existing rules to support the new location.

/data/backup -> /data/system_ce/[user id]/backup
Previously covered by rule backup_data_file

/cache/backup -> /data/system_ce/[user id]/backup_stage
Previously covered by rule cache_backup_file

Also add support for vold to create and perform restorecon on the new
locations.

Example denials and detailed proposal in the doc on the linked bug.

Bug: 121197420
Test: 1) Boot device; check dirs created with correct label; run backup
successfully on system user
2) Create secondary user; check dirs created with correct label; run
backup successfully

Change-Id: I47faa69cd2a6ac55fb762edbf366a86d3b06ca77