Update tools to python3 (#85)

This updates the scripts in the tools directory to work with python3, python2
support is now deprecated.

The only significant API change is that the subprocess module works in bytes
instead of str, the rest are mainly style changes.
diff --git a/tools/known_test_failures.py b/tools/known_test_failures.py
index 262d6e6..791568b 100644
--- a/tools/known_test_failures.py
+++ b/tools/known_test_failures.py
@@ -76,7 +76,7 @@
     'AARCH64_SIM_frsqrts_D'
   }
 
-  filtered_list = filter(lambda x: x not in known_valgrind_test_failures, tests)
+  filtered_list = [x for x in tests if x not in known_valgrind_test_failures]
   return (filtered_list, len(tests) - len(filtered_list), reason)
 
 def FilterKnownTestFailures(tests, **env):