Fix docs build failure with sphinx 1.5 and python3
Fix docs build failure with sphinx 1.5 and python3

Change-Id: I439561ba681591f5f683aed2f4c2718260746c7c
Closes-Bug: #1673720

openstack/stackalytics,stackforge/stackalytics,0xf2/stackalytics,0xf2/stackalytics,stackforge/stackalytics,openstack/stackalytics,openstack/stackalytics,stackforge/stackalytics,0xf2/stackalytics,openstack/stackalytics,0xf2/stackalytics