[lint] Fix lint to not raise an exception at the end.

recipe_engine/lint_test.py

Index: recipe_engine/lint_test.py
diff --git a/recipe_engine/lint_test.py b/recipe_engine/lint_test.py
index 38772e624944bb6245fe16761260948f5da68ce6..07ca34b79d5706026f66c511f3f2d745855fb023 100755
--- a/recipe_engine/lint_test.py
+++ b/recipe_engine/lint_test.py
@@ -18,6 +18,7 @@ import types
 
 
 MODULES_WHITELIST = [
+  r'ast',
   r'base64',
   r'collections',
   r'contextlib',
@@ -34,14 +35,6 @@ MODULES_WHITELIST = [
 ]
 
 
-class ImportViolationError(Exception):
-  pass
-
-
-class TestFailure(Exception):
-  pass
-
-
 def ImportsTest(recipe_path, recipe_name, whitelist, universe_view):
   """Tests that recipe_name only uses allowed imports.
 
@@ -89,4 +82,7 @@ def main(package_deps, args):
         ImportsTest(recipe_path, recipe_name, whitelist, universe_view))
 
   if errors:
-    raise TestFailure('\n'.join(map(str, errors)))
+    for line in map(str, errors):
+      print line
+    return 1
+  return 0