sepolicy: add rules for updater and update_engine

* We need special exceptions for update_engine scripts because we
  handle backuptool operations through it.

* priv_app needs to be able to make ota package dirs in order to
  put the ota in the correct spot.

Change-Id: I39d9d43ea4eb9e567c6ee24a4cd4f8969cd2bcdd
diff --git a/sepolicy/private/file_contexts b/sepolicy/private/file_contexts
new file mode 100644
index 0000000..40295bb
--- /dev/null
+++ b/sepolicy/private/file_contexts
@@ -0,0 +1,4 @@
+# Postinstall
+/system/bin/backuptool_ab\.functions              u:object_r:otapreopt_chroot_exec:s0
+/system/bin/backuptool_ab\.sh                     u:object_r:otapreopt_chroot_exec:s0
+/system/bin/backuptool_postinstall\.sh            u:object_r:otapreopt_chroot_exec:s0