Set empty watchlist test config before CTS

Test: CTS pass
Bug: 63908748
Change-Id: I8b607feb44f873aced1ae3c2ff02c02f0553fb10
diff --git a/tests/cts/net/Android.mk b/tests/cts/net/Android.mk
index e67bb8f..1430071 100644
--- a/tests/cts/net/Android.mk
+++ b/tests/cts/net/Android.mk
@@ -45,7 +45,8 @@
     ctstestrunner \
     ctstestserver \
     mockwebserver \
-    junit
+    junit \
+    truth-prebuilt
 
 # uncomment when b/13249961 is fixed
 #LOCAL_SDK_VERSION := current