Root of /data belongs to init (re-landing)

Give /data itself a different label to its contents, to ensure that
only init creates files and directories there.

This change originally landed as aosp/1106014 and was reverted in
aosp/1116238 to fix b/140402208. aosp/1116298 fixes the underlying
problem, and with that we can re-land this change.

Bug: 139190159
Bug: 140402208
Test: aosp boots, logs look good
Change-Id: I1a366c577a0fff307ca366a6844231bcf8afe3bf
diff --git a/private/file_contexts b/private/file_contexts
index 3740218..1e9549c 100644
--- a/private/file_contexts
+++ b/private/file_contexts
@@ -436,7 +436,8 @@
 # NOTE: When modifying existing label rules, changes may also need to
 # propagate to the "Expanded data files" section.
 #
-/data(/.*)?		u:object_r:system_data_file:s0
+/data		u:object_r:system_data_root_file:s0
+/data/(.*)?		u:object_r:system_data_file:s0
 /data/system/packages\.list u:object_r:packages_list_file:s0
 /data/unencrypted(/.*)?         u:object_r:unencrypted_data_file:s0
 /data/backup(/.*)?		u:object_r:backup_data_file:s0