[all] stable branch integration gates are pulling artifacts from master

[Samuel Cassiba]

In http://logs.openstack.org/37/356037/1/check/gate-cookbook-openstack-identity-chef-rake-integration-ubuntu-trusty-nv/16c562c/console.html it was found that artifacts are being sourced from the master branch, instead of the correct stable branch (in this case, stable/mitaka).

2016-08-19 12:55:26.338558 | + chef exec rake integration
2016-08-19 12:55:26.689268 | wget -nv -t 3 -O Rakefile-Common https://raw.githubusercontent.com/openstack/cookbook-openstack-common/master/Rakefile
2016-08-19 12:55:26.853949 | 2016-08-19 12:55:26 URL:https://raw.githubusercontent.com/openstack/cookbook-openstack-common/master/Rakefile [1425/1425] -> "Rakefile-Common" [1]