Environment creation from skeleton is not tested

[priteau]

I just hit this issue caused by lack of escaping in the skeleton template:

Unable to create file 'inventory/group_vars/all/alertmanager.yml'
Error message: 'vault_alertmanager_slack_integration_app_creds' is undefined

I have opened #682 to fix it, but could we test environment creation in CI?

[sjpb]

We can add it to the massive list of things to do, yes 😆