Fix: exit code is 0 even when check-boot-jars.py fails

Fix the bug that build is still success when boot jars contain
non-whitelisted classes. Now, check-boot-jars.py correctly
finishes with exit code 1 when non-whitelisted classes are found.

Change-Id: Id5c80ef9fdb70213d878d569f6033be2c9eb90d3

core/tasks/check_boot_jars/check_boot_jars.py

@@ -64,10 +64,10 @@ def CheckJar(jar):
 def main(argv):
   if len(argv) < 2:
     print __doc__
-    sys.exit(1)
+    return 1
 
   if not LoadWhitelist(argv[0]):
-    sys.exit(1)
+    return 1
 
   passed = True
   for jar in argv[1:]:
@@ -80,4 +80,4 @@ def main(argv):
 
 
 if __name__ == '__main__':
-  main(sys.argv[1:])
+  sys.exit(main(sys.argv[1:]))