[RFC] Building travis ci container

[joelwurtz]

There is 3 way to build travis ci container :
#1. Keep it the current way

Keep the current implementation with Dockerfile and try to make container as close as their vms

Pro : Can have fast container build
Con : Must follow and support change to travis ci boxes
#2. Use travis cookbooks

Use https://github.com/travis-ci/travis-cookbooks with some commands to build vms

Pro : Very close to travis ci VM, less work to support change
Con : Take a HUGE time for the first build and will be pretty heavy in size
#3. Use travis cookbooks + docker registry

Same as 2. but container are pre-built into image and push to docker public registry

Pro : No built time, only download time
Con : Always pretty heavy in size, require more tooling for upgrade mechanism

If some people have better options, i will be glade to hear them.

[joelwurtz]

Decision :

Keep it the current way with twig generator and generate a maximum of thing in pre built images to match travis at this repo https://github.com/jolicode/docker-images