Allow shell to read VAB props.

Bug: 179427873
Test: adb unroot and read the prop
Change-Id: Ib480903afae2e7180a59f8834dd7c54062acd947
diff --git a/private/shell.te b/private/shell.te
index 3ca8360..94a2c2e 100644
--- a/private/shell.te
+++ b/private/shell.te
@@ -183,3 +183,6 @@
 
 # Allow shell to read the dm-verity props on user builds.
 get_prop(shell, verity_status_prop)
+
+# Allow shell to read Virtual A/B related properties
+get_prop(shell, virtual_ab_prop)