convert to print_function

BUG=chromium:414895
TEST=`./cbuildbot/run_tests` passes
TEST=`cros lint` passes (it complains if print is used incorrectly)
TEST=`cbuildbot chromiumos-sdk` passes
TEST=`cbuildbot lumpy-release` passes

Change-Id: I67e7e1290b03a16525e0c2b1afa74ebbd8d3508f
Reviewed-on: https://chromium-review.googlesource.com/218572
Reviewed-by: David James <davidjames@chromium.org>
Reviewed-by: Yu-Ju Hong <yjhong@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/cros_env_whitelist.py b/scripts/cros_env_whitelist.py
index 3eae1ab..83c329e 100644
--- a/scripts/cros_env_whitelist.py
+++ b/scripts/cros_env_whitelist.py
@@ -4,8 +4,10 @@
 
 """Print the environment whitelist."""
 
+from __future__ import print_function
+
 from chromite.cbuildbot import constants
 
 
 def main(_argv):
-  print ' '.join(constants.CHROOT_ENVIRONMENT_WHITELIST)
+  print(' '.join(constants.CHROOT_ENVIRONMENT_WHITELIST))