-i, -i support for exec-as

[Andrew]

Is your feature request related to a problem? Please describe.

Please support conventional -i, -t flags for exec-as, so that the command is able to support interactive shell sessions, just like kubectl exec.

Describe the solution you'd like

Implement -i and -t.

Describe alternatives you've considered

Skipping the exec-as plugin altogether and diving into the node.

[Jordan Wilson]

@mcandre I still need to do some more work on it to properly support the -c flag but can you try the kubectl ssh plugin (from master) and let me know if that is working for you? Thanks.