Move staged backup content to a specific cache subdir

Also narrowly specify the domain for the local transport's bookkeeping.

Bug 26834865

Change-Id: I2eea8a10f29356ffecabd8e102f7afa90123c535
diff --git a/file_contexts b/file_contexts
index 55212d4..f292780 100644
--- a/file_contexts
+++ b/file_contexts
@@ -319,11 +319,12 @@
 # Cache files
 #
 /cache(/.*)?		u:object_r:cache_file:s0
-/cache/.*\.data	u:object_r:cache_backup_file:s0
-/cache/.*\.restore	u:object_r:cache_backup_file:s0
-# LocalTransport (backup) uses this directory
-/cache/backup(/.*)?	u:object_r:cache_backup_file:s0
 /cache/recovery(/.*)?	u:object_r:cache_recovery_file:s0
+# General backup/restore interchange with apps
+/cache/backup_stage(/.*)?	u:object_r:cache_backup_file:s0
+# LocalTransport (backup) uses this subtree
+/cache/backup(/.*)?		u:object_r:cache_private_backup_file:s0
+
 #############################
 # sysfs files
 #