Fix build warning.

(cherry-picked from e79ac583cf570e66762c93c9bdfea14fd5c6249a)

Change-Id: I76cc3e709606b9e58e2f5c639207ffb53462905b
diff --git a/JavaLibrary.mk b/JavaLibrary.mk
index 18fa870..4d91adb 100644
--- a/JavaLibrary.mk
+++ b/JavaLibrary.mk
@@ -151,7 +151,7 @@
     LOCAL_JAVA_LIBRARIES := bouncycastle-hostdex core-hostdex core-junit-hostdex
     LOCAL_STATIC_JAVA_LIBRARIES := sqlite-jdbc-host mockwebserver-hostdex
     LOCAL_JAVACFLAGS := $(local_javac_flags)
-    LOCAL_MODULE_TAGS := tests
+    LOCAL_MODULE_TAGS := optional
     LOCAL_MODULE := core-tests-hostdex
     LOCAL_NO_EMMA_INSTRUMENT := true
     LOCAL_NO_EMMA_COMPILE := true