Run provisioning steps at machine creation

[dlespiau]

Extracted from #76

footloose could run provisioning commands when creating a machine. That means we could run an ansible playbook on machine creation automatically.

Of course there are security concerns and we shouldn't allow to execute arbitrary commands. By default I think we shouldn't allow any command to be run unless the user tells us it's ok:

$ footlose create --allow-provisioning=ansible # <- name(s) of the command(s) the user allows us to exec.

[dlespiau]

Alternatively, we could take a page from the terraform book and expose each provisionner specifically: https://www.terraform.io/docs/provisioners/index.html.

I think I like that better :)

[ilmanzo]

+1 for a "provisioner" config entry with many options: "ansible", "local-exec", "puppet" and so on, each provisioner should have its arguments of course