Prepare for removal of legacy-test from default targets

In preparation for removing junit classes from the Android API
the legacy-test target will be removed from the
TARGET_DEFAULT_JAVA_LIBRARIES. This change adds explicit
dependencies on junit and/or legacy-android-test to ensure that
modules will compile properly once it is removed.

Bug: 30188076
Test: make checkbuild
Change-Id: Ie8aeb9206c38685abe3b72a0b80bd0faa5ddb9ce
diff --git a/tests/Android.mk b/tests/Android.mk
index ba6944d..850aca3 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -33,6 +33,7 @@
         android-support-test \
         mockito-target-minus-junit4 \
         espresso-core \
-        truth-prebuilt
+        truth-prebuilt \
+        legacy-android-test
 
 include $(BUILD_PACKAGE)