Add type for directories containing snapshots of apex data.

This adds a new apex_rollback_data_file type for the snapshots (backups)
of APEX data directories that can be restored in the event of a rollback.

Permission is given for apexd to create files and dirs in those directories
and for vold_prepare_subdirs to create the directories.

See go/apex-data-directories for details.

Bug: 141148175
Test: Built and flashed, checked directory was created with the correct
type.

Change-Id: I94b448dfc096e5702d3e33ace6f9df69f58340fd
diff --git a/private/file_contexts b/private/file_contexts
index 6ffbf10..26f4586 100644
--- a/private/file_contexts
+++ b/private/file_contexts
@@ -496,6 +496,7 @@
 # Misc data
 /data/misc/adb(/.*)?            u:object_r:adb_keys_file:s0
 /data/misc/apexdata(/.*)?       u:object_r:apex_module_data_file:s0
+/data/misc/apexrollback(/.*)?   u:object_r:apex_rollback_data_file:s0
 /data/misc/apns(/.*)?           u:object_r:radio_data_file:s0
 /data/misc/audio(/.*)?          u:object_r:audio_data_file:s0
 /data/misc/audioserver(/.*)?    u:object_r:audioserver_data_file:s0
@@ -583,6 +584,10 @@
 /data/misc_de/[0-9]+/apexdata(/.*)?       u:object_r:apex_module_data_file:s0
 /data/misc_ce/[0-9]+/apexdata(/.*)?       u:object_r:apex_module_data_file:s0
 
+# Apex rollback directories
+/data/misc_de/[0-9]+/apexrollback(/.*)?   u:object_r:apex_rollback_data_file:s0
+/data/misc_ce/[0-9]+/apexrollback(/.*)?   u:object_r:apex_rollback_data_file:s0
+
 #############################
 # Expanded data files
 #