[cern] Fix DC/OS
- DCOS and mesos have the same validation methods but in out cherry-pick it was skipped [1].
- Add missing init.py
- Remove neutron resources
- Add staging rpm
Related-Ticket: OS-5206
[1] https://review.openstack.org/#/c/475682/8/magnum/api/validation.py@213
Edited by Spyridon Trigazis