ART: Run Checker with Python >2.6

Chromium buildbots don't have Python 3. This patch fixes the uses
of print() and ASCII vs. Unicode strings to make Checker compatible
with Python 2.6 and above.

Change-Id: Ic065d990f668b8cf95a337aae037699e8474fcee
diff --git a/tools/checker.py b/tools/checker.py
index b71eac6..55f015e 100755
--- a/tools/checker.py
+++ b/tools/checker.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python3
+#!/usr/bin/env python2
 #
 # Copyright (C) 2014 The Android Open Source Project
 #
@@ -71,6 +71,7 @@
 #   constant folding returns an integer constant with value either 11 or 22.
 #
 
+from __future__ import print_function
 import argparse
 import os
 import re