Build AVB host test conditionally

To test hermetic builds of Trusty, limit building of host test to
test builds.

Bug: 199946160
Change-Id: Ie067346afa6943ec210c1e98ac8fce1f12d5f725
diff --git a/rules.mk b/rules.mk
index 1f19e4e..83623d4 100644
--- a/rules.mk
+++ b/rules.mk
@@ -34,7 +34,9 @@
 	trusty/user/base/lib/storage \
 
 # Build the test.
+ifeq (true,$(call TOBOOL,$(TEST_BUILD)))
 MODULE_DEPS += trusty/user/app/avb/test
+endif
 
 MODULE_INCLUDES += \
 	$(LOCAL_DIR)