memoized: detect hashability by catching TypeError

This is a fix for

https://github.com/ARM-software/devlib/issues/60

Apprently, being an instance of Hashable does not mean that the object
is, in fact, hashable. So rather than testing for hashability, try to
hash the object and handle the potential error by falling back to the
old method.

devlib/utils/misc.py

@@ -33,7 +33,6 @@ import ctypes
 from operator import itemgetter
 from itertools import groupby
 from functools import partial
-from collections import Hashable
 
 import wrapt
 
@@ -558,9 +557,9 @@ def __get_memo_id(obj):
     ID string.
     """
     obj_id = id(obj)
-    if isinstance(obj, Hashable):
+    try:
         return '{}/{}'.format(obj_id, hash(obj))
-    else:
+    except TypeError:  # obj is not hashable
         obj_pyobj = ctypes.cast(obj_id, ctypes.py_object)
         # TODO: Note: there is still a possibility of a clash here. If Two
         # different objects get assigned the same ID, an are large and are