[k8s] sky check k8s fails when current context is not available, even if that context is not in allowed_contexts

[cg505]

~/.sky/config.yaml:

kubernetes:
  allowed_contexts:
    - kind-skypilot

current context:

$ kubectl config current-context
gke-dev

kind-skypilot cluster is up, but gke-dev cluster is down.

Expected behavior:
When kubernetes.allowed_contexts is set in ~/.sky/config.yaml, sky check k8s should check if any of these contexts are available. (or, maybe if they are all available)
In this example, it should succeed since kind-skypilot is available.

Actual behavior:
sky check k8s will succeed if and only if the kubernetes current context (given by kubectl config current-context) is available, even if that context is not present in the list of allowed_contexts and all allowed_contexts are available.
In this example, it will fail since gke-dev is not available.

Version & Commit info:

• sky -v: skypilot, version 1.0.0-dev0
• sky -c: skypilot, commit a63eaf5-dirty