According to Openstack summit session ,
stestr is maintained project to which all Openstack projects should migrate.
Let's switch to stestr as other projects have already moved to it.
We clean up oslo-incubator in 90ae25e389,
There are some obsolete things to clean.
* Remove api maintainers file and check script
* Remove sync tool with copy code to other openstack project.
* Remove graduate script
* remove section entry_points in setup.cfg
* Clean test related stuff in tox.ini
* Remove requirements.txt/test-requirements.txt
The requirements list for the release tools keeps growing, so start
managing it separately and use tox as a front-end to create a virtualenv