Introduce bash completions for kubecfg

completions only work for list, get, create, delete.
I don't think this works by itself... I guess you stole this from some code that was setting "comps" and later on using it on a compgen call :-)

```shell
  local comps=$(compgen -A hostname)
  COMPREPLY=( $(compgen -W "${comps}" -- "$cur") )
```