Move tooz from Stackforge to OpenStack

The Oslo program is adopting tooz according to
  https://review.openstack.org/#/c/122439/
  https://review.openstack.org/#/c/135265/

The project is gated against Python 2.6 too because it's already being
usde by at least the Juno release of Ceilometer.

This also fixes the link between Gerrit and Launchpad.

Blueprint: tooz-adoption

Change-Id: Iab7eff71e06cfc7ffe3fa8d99385c34a0a18f3d3
Merge "Move tooz from Stackforge to OpenStack"