Fix error printing of missing file/dir in apk compare

Change-Id: I38118f334e3ea5a64d8dfc40e37510590e682d0a
diff --git a/tools/compare_apk_sizes.py b/tools/compare_apk_sizes.py
index da505c7..9a56187 100755
--- a/tools/compare_apk_sizes.py
+++ b/tools/compare_apk_sizes.py
@@ -45,7 +45,7 @@
 def ensure_exists(files):
   for f in files:
     if not os.path.exists(f):
-      raise Exception('%s does not exist')
+      raise Exception('%s does not exist' % f)
 
 def extract_classes(input, output):
   if os.path.exists(output):