testsys: Support environment kubecontext

[ecpullen]

Issue number:

Closes #2426

Description of changes:

Enables testsys to use an environments kubeconfig if the kubeconfig path doesn't exist.

Testing done:

Tested with kubeconfig in testsys.kubeconfig and with kind create cluster.

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.