Baseline changes to comply with Release Notes Management
based in Reno :
* Use build-openstack-releasenotes job for release notes
(We can't use the OpenStack releasenotes template as it includes
publish jobs, stx needs its own)
* Add newnote tox environment as convenience for creating new release
notes, re-using the releasenotes venv.
* Remove the unused 'true' tox environment.
Signed-off-by: Abraham Arce <firstname.lastname@example.org>