Allow update_engine to get gsid property

Allow the update_engine to use the gsid property and to avoid the VAB
merge when running a DSU.

Bug:147071959
Test: ota_e2etest.py

Change-Id: I4a8d179e7e71f74d0c7ad34767de1f619f134d20
diff --git a/prebuilts/api/30.0/public/update_engine.te b/prebuilts/api/30.0/public/update_engine.te
index 078e494..8b767be 100644
--- a/prebuilts/api/30.0/public/update_engine.te
+++ b/prebuilts/api/30.0/public/update_engine.te
@@ -69,6 +69,9 @@
 # Allow to set the OTA related properties, e.g. ota.warm_reset.
 set_prop(update_engine, ota_prop)
 
+# Allow to get the DSU status
+get_prop(update_engine, gsid_prop)
+
 # update_engine tries to determine the parent path for all devices (e.g.
 # /dev/block/by-name) by reading the default fstab and looking for the misc
 # device. ReadDefaultFstab() checks whether a GSI is running by checking