Turn find emulator warnings into errors

Test: build/soong/build_test.bash (multiproduct_kati)
Change-Id: Ieb65a457c8c1ed4bff44a01aa2cc11203172ba9b
diff --git a/ui/build/kati.go b/ui/build/kati.go
index 972b559..48c38d4 100644
--- a/ui/build/kati.go
+++ b/ui/build/kati.go
@@ -74,6 +74,7 @@
 		"--detect_android_echo",
 		"--color_warnings",
 		"--gen_all_targets",
+		"--werror_find_emulator",
 		"-f", "build/core/main.mk",
 	}