Add support for openstack provider (#1103)

[pascal-hofmann]

This PR adds support for openstack and closes #1103.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[pascal-hofmann]

There were some bogus / missing tests. These are fixed / added now. Ready for review.

[gruebel]

thanks for the great addition 🚀, I just found some minor things

[nimrodkor]

thanks @pascal-hofmann !!

[pascal-hofmann]

Thanks for the quick review/merge!

[MindTooth]

It's great to see OpenStack support, but saying that no hardcoded value is somewhat lacking and then not provide the best approach.

My use case is that I use a variable that's exported via an environment variable or a terraform.tfvars. Meaning, no hardcoded value exists. application_credential_secret = var.os_application_credential_secret is not hardcoded, IMHO. If this is not enough, I'm eager to learn why.

---

I want to be absolutely clear, I love that OpenStack is supported. I work with OS almost daily. Thank you. 👍🏻

[gruebel]

@MindTooth great question, you can expose them through plain old environment variables and don't need to reference them in the provider

• token -> OS_TOKEN or OS_AUTH_TOKEN
• password -> OS_PASSWORD
• application_credential_secret -> OS_APPLICATION_CREDENTIAL_SECRET fun fact this is not documented in the Terraform provider, but I took a look into source code 😄

I hope that helps 🙂

[MindTooth]

Just wanted to drop by and let you know that the following works great:

• OS_AUTH_TYPE=v3applicationcredential
• OS_AUTH_URL=
• OS_APPLICATION_CREDENTIAL_ID=
• OS_APPLICATION_CREDENTIAL_SECRET=

I've converted almost all my projects to use only these. Note! Important that no other OS_ variables are set. As application credentials are scoped, they only work for one project. Also, this removes the need for a provider "openstack" {} block.