Add deploy files to create a new TLJH instance with the gallery

[jtpio]

This PR adds a few configuration files to deploy a new version of the gallery to OVH without having to click through the UI or manually SSH to the machine.

This takes the current design into account:

• deployed on a single instance
• using TLJH + plugin system

TODO

• Add deploy.py file
• Add logging
• Add dry-run mode
• Fix FIXMEs

Other options to consider would be:

• Terraform: need to share the state in some way
• Ansible: is it worth the effort?
• Make the gallery work on Kubernetes using KubeSpawner? Interesting for the long term, but it would also add a bit of complexity: building and pushing the images to a registry, extending the ZTJH helm chart or creating its own...

[jtpio]

This still needs some iteration of course but we can start discussing what the best approach would be.

[jtpio]

An example log (not waiting for the Docker images to be ready):

$ python deploy.py --tag c0ab38a
2019-07-15 10:15:41,259 - Connect...
2019-07-15 10:15:41,275 - Connected
2019-07-15 10:15:41,275 - List existing servers
2019-07-15 10:15:44,291 - Create server voici-gallery-c0ab38a-95e457...
2019-07-15 10:15:45,994 - Server created: f16fac94-7a4e-443f-bf95-6093fa488b52
2019-07-15 10:15:45,994 - Check server is ACTIVE: f16fac94-7a4e-443f-bf95-6093fa488b52
2019-07-15 10:15:56,125 - Check server is ACTIVE: f16fac94-7a4e-443f-bf95-6093fa488b52
2019-07-15 10:16:06,242 - Check server is ACTIVE: f16fac94-7a4e-443f-bf95-6093fa488b52
2019-07-15 10:16:16,406 - Check server is ACTIVE: f16fac94-7a4e-443f-bf95-6093fa488b52
2019-07-15 10:16:26,682 - Check server is ACTIVE: f16fac94-7a4e-443f-bf95-6093fa488b52
2019-07-15 10:16:27,255 - Server f16fac94-7a4e-443f-bf95-6093fa488b52 is ACTIVE
2019-07-15 10:16:27,644 - Poll http://51.68.114.136/api
2019-07-15 10:17:07,488 - Poll http://51.68.114.136/api
2019-07-15 10:17:38,277 - Poll http://51.68.114.136/api
2019-07-15 10:18:09,075 - Poll http://51.68.114.136/api
2019-07-15 10:18:39,740 - Poll http://51.68.114.136/api
2019-07-15 10:19:10,551 - Poll http://51.68.114.136/api
2019-07-15 10:19:41,288 - Poll http://51.68.114.136/api
2019-07-15 10:20:12,084 - Poll http://51.68.114.136/api
2019-07-15 10:20:43,306 - Poll http://51.68.114.136/api
2019-07-15 10:21:14,125 - Poll http://51.68.114.136/api
2019-07-15 10:21:44,989 - Poll http://51.68.114.136/api
2019-07-15 10:22:15,952 - Poll http://51.68.114.136/api
2019-07-15 10:22:46,616 - Poll http://51.68.114.136/api