Fix cloudkitty exception handling from gnocchiclient
Fix cloudkitty exception handling from gnocchiclient

Probably due six removal, exception handling from gnocchiclient
in cloudkitty is not working as expected.

This patch fixing this issue.

Bug described in storyboard:
https://storyboard.openstack.org/#!/story/2008985

Story: 2008985
Task: 42635
Change-Id: I387fee79d277daa4c739297f1734dad1eaf4cc94

openstack/cloudkitty,openstack/cloudkitty