Replace oslo_utils.encodeutils.exception_to_unicode

The function is being deprecated now because it is equivalent to
str(ex) in Python 3.

Depends-on: https://review.opendev.org/c/openstack/oslo.utils/+/938929
Change-Id: I7c9ca3730e1ab6ffdaf8cb78c002ac4e157fe2f1

glanceclient/v2/images.py

@@ -408,7 +408,7 @@ class Controller(object):
             try:
                 setattr(image, key, value)
             except warlock.InvalidOperation as e:
-                raise TypeError(encodeutils.exception_to_unicode(e))
+                raise TypeError(str(e))
 
         resp, body = self.http_client.post(url, headers=headers, data=image)
         # NOTE(esheffield): remove 'self' for now until we have an elegant
@@ -443,7 +443,7 @@ class Controller(object):
             try:
                 setattr(image, key, value)
             except warlock.InvalidOperation as e:
-                raise TypeError(encodeutils.exception_to_unicode(e))
+                raise TypeError(str(e))
 
         if remove_props:
             cur_props = image.keys()