Re-label /data/pkg_staging files as staging.

While the directory is not present anymore in Q, it has been shipped on
Q Beta 2 and the absence of such label might cause issues to devices
with pending installs which receive an OTA > Beta 2.

Bug: 130184133
Test: m
Change-Id: Ie3e77eebd2e7fd7b3a6a940d189cbc2bb386dc0e
diff --git a/private/file_contexts b/private/file_contexts
index f3f367b..f4aefe3 100644
--- a/private/file_contexts
+++ b/private/file_contexts
@@ -451,6 +451,8 @@
 /data/mediadrm(/.*)?	u:object_r:media_data_file:s0
 /data/nativetest(/.*)?	u:object_r:nativetest_data_file:s0
 /data/nativetest64(/.*)?	u:object_r:nativetest_data_file:s0
+# This directory was removed after Q Beta 2, but we need to preserve labels for upgrading devices.
+/data/pkg_staging(/.*)?		u:object_r:staging_data_file:s0
 /data/property(/.*)?	u:object_r:property_data_file:s0
 /data/preloads(/.*)?	u:object_r:preloads_data_file:s0
 /data/preloads/media(/.*)?	u:object_r:preloads_media_file:s0