Handle error response for webob>=1.6.0

WebOb change https://github.com/Pylons/webob/pull/230 changed
the way in which the error response body is formatted such that
it's no longer a nested dict. So we have to handle both the
old convention of an error message key to the response body error
dict and the new way with just the error body dict.

This was reported upstream:

https://github.com/Pylons/webob/issues/235

But given this was apparently implemented as a long-overdue change
in WebOb the behavior is not likely to change.Handle error response for
webob>=1.6.0

Change-Id: I7d589415aa024588faf77c8234ac026110f6c3cd
Closes-Bug: #1559072
(cherry picked from commit 19befa6965)

cinderclient/exceptions.py

@@ -242,9 +242,14 @@ def from_response(response, body):
         message = "n/a"
         details = "n/a"
         if hasattr(body, 'keys'):
-            error = body[list(body)[0]]
-            message = error.get('message', message)
-            details = error.get('details', details)
+            # Only in webob>=1.6.0
+            if 'message' in body:
+                message = body.get('message')
+                details = body.get('details')
+            else:
+                error = body[list(body)[0]]
+                message = error.get('message', message)
+                details = error.get('details', details)
         return cls(code=response.status_code, message=message, details=details,
                    request_id=request_id, response=response)
     else: