Get kubernetes version for all cloud providers + pytest refactor

[iameskild]

Fixes | Closes | Resolves #854 #628

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Changes:

Besides adding/updating kubernetes_versions functions for all the cloud providers, I have made the following motivated changes:

• Standardized how all of the kubernetes_versions functions behave. For all cloud providers, they return a list of available kubernetes versions from oldest to latest.
  • To avoid having to set cloud credentials and using the cloud provider SDK, set QHUB_K8S_VERSION environment variable.
• If the user doesn't specify a kubernetes version during qhub init, the latest available version will be used.
• If the user tries to specify an "unsupported" version, it will cause a ValueError
  • Now each render_config (qhub init and qhub render) will check the kubernetes version using the cloud provider SDK. This will require setting the appropriate credentials.
• Updates to test suite include a setup_fixture which can be reused for any test that calls render_config, reducing the amount of duplicated code.

Types of changes

What types of changes does your code introduce?

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds a feature)
• Breaking change (fix or feature that would cause existing features to not work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
• Other (please describe):

Testing

Requires testing

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• No

In case you checked yes, did you write tests?

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• No

Large test suit refactor.

Further comments (optional)

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[viniciusdc]

LGTM, but as I was already tired in the end, it should be interesting to have someone else inspect the pytest parts XD. But in general, that's an amazing job, thanks @iameskild !!!!

[viniciusdc]

Is it possible to add the Kubernetes version checker here?

### Verify Kubernetes version
_set_kubernetes_version(config, kubernetes_version, cloud_provider)

Then we could have just one call for it, and remove it from the conditionals above

[iameskild]

@viniciusdc the current state requires that cloud_provider be passed to the _set_kubernetes_version which means we can't simply replace all of these functions calls with one call. We might be able to do something like:

for cloud_provider in ["aws", "do", "azure", "gcp", "local"]:
    _set_kubernetes_version(config, kubernetes, cloud_provider)

[viniciusdc]

LGTM, but it would be good to have someone else to have a look as well

[danlester]

Excellent, thank you!