Add etc -> system/etc symlink for cgroups

Bug: 185186899
Test: run microdroid and see log
Change-Id: I1ac7639f32f3dcc4d703ee752d015946ead00e8f
diff --git a/microdroid/Android.bp b/microdroid/Android.bp
index 2522679..249ddc7 100644
--- a/microdroid/Android.bp
+++ b/microdroid/Android.bp
@@ -30,6 +30,10 @@
         target: "/sys/kernel/debug",
         name: "d",
     },
+    {
+        target: "/system/etc",
+        name: "etc",
+    },
 ]
 
 android_system_image {