Use ast.literal_eval instead of json.loads to avoid unicode problems on windows
diff --git a/tools/run_tests/run_tests.py b/tools/run_tests/run_tests.py
index e31fc30..6e4a149 100755
--- a/tools/run_tests/run_tests.py
+++ b/tools/run_tests/run_tests.py
@@ -480,7 +480,7 @@
 
 # different configurations we can run under
 with open('tools/run_tests/configs.json') as f:
-  _CONFIGS = dict((cfg['config'], Config(**cfg)) for cfg in json.loads(f.read()))
+  _CONFIGS = dict((cfg['config'], Config(**cfg)) for cfg in ast.literal_eval(f.read()))
 
 
 _DEFAULT = ['opt']