Allow update_engine, recovery, and fastbootd to read snapuserd properties.

Bug: 193833730
Test: OTA applies and boots
Change-Id: I81c089e1763a7e25b23df245f76e04acd52a337e
diff --git a/private/fastbootd.te b/private/fastbootd.te
index 40b3945..2c65281 100644
--- a/private/fastbootd.te
+++ b/private/fastbootd.te
@@ -22,6 +22,7 @@
   # Determine allocation scheme (whether B partitions needs to be
   # at the second half of super.
   get_prop(fastbootd, virtual_ab_prop)
+  get_prop(fastbootd, snapuserd_prop)
 
   # Needed for TCP protocol
   allow fastbootd node:tcp_socket node_bind;