Switch to ast.literal_eval for dict parsing

Due to  some test data in the BDD feature files includes Python raw strings and escape sequences that standard json.loads() cannot parse switching to safer Python literal evaluation
for converting string representations of dictionaries.

test/bdd/utils/checks.py

@@ -7,6 +7,7 @@
 """
 Helper functions to compare expected values.
 """
+import ast
 import collections.abc
 import json
 import re
@@ -58,7 +59,8 @@ COMPARISON_FUNCS = {
     None: lambda val, exp: str(val) == exp,
     'i': lambda val, exp: str(val).lower() == exp.lower(),
     'fm': lambda val, exp: re.fullmatch(exp, val) is not None,
-    'dict': lambda val, exp: val is None if exp == '-' else (val == json.loads('{' + exp + '}')),
+    'dict': lambda val, exp: (val is None if exp == '-'
+                              else (val == ast.literal_eval('{' + exp + '}'))),
     'in_box': within_box
 }