Make enos/master follows kolla-ansible/last-stable

[rcherrueau]

The current enos/master branch tries to follow the kolla-ansible/master, but the project momentum makes it difficult. One solution would be to follow the kolla-ansible/last-stable (e.g, kolla-ansible/stable/rocky).

Thus, we have to change branches structure of the project:

1. Put the actual master branch into a new one called develop (in order to keep inventory/password update commits, if need be. We can remove it afterwards)
2. Build the new master starting from enos/stable/queens and make it follows kolla-ansible/stable/rocky
3. Push new commits to enos/master and back-port them to enos/stable/queens
4. (Release enos/stable/rocky at the time of kolla-ansible/stable/stein)

To achieve this we have to:

• Update the documentation to reflect the new structure (in both stable/queens and master)
• Change the branches structure as explained above