[test] functional framework: add CScript hex() for Python 3.4

test/functional/wallet_importmulti.py failed with:
AttributeError: 'CScript' object has no attribute 'hex'

test/functional/test_framework/script.py

@@ -450,6 +450,10 @@ def join(self, iterable):
         # join makes no sense for a CScript()
         raise NotImplementedError
 
+    # Python 3.4 compatibility
+    def hex(self):
+        return hexlify(self).decode('ascii')
+
     def __new__(cls, value=b''):
         if isinstance(value, bytes) or isinstance(value, bytearray):
             return super(CScript, cls).__new__(cls, value)