Export KUBECONFIG to current terminal's session

[ibreakthecloud]

Describe the bug

• cmd/cluster_use.go is trying to set env var, using os.Setenv() which is only accessible inside program, i.e. child process.
  Possible Explanation: A process has a copy of its parent's environment and can't write to the parent environment.
  Process Tree:

`--- shell
          `--- go program
          |
          `--- other program

Expected behavior
It is suppose the set the env variable KUBECONFIG in terminal.
os/exec can be used in this scenario, but the major drawback can be export is not a binary.

[devinburnette]

I don't think it's possible to change the environment of the parent process, but there are other ways to set the active KUBECONFIG cluster.

If there's no KUBECONFIG environment variable set, then kubectl will also look in the default place which is ~/.kube/config. Have you thought about having use set or change a sym link that points to the selected cluster config?

[ibreakthecloud]

@devinburnette Thanks for the suggestion, I haven't tried this one, I'll look into it, in the mean time if you can fix this, it will be highly appreciated!