oc vs kubectl flexibility

[trent-s]

Currently susql uses both oc and kubectl in various scripts:

It would be cleaner to do the following:

• If either OC or KUBECTL env variables is specified, assume it is a file location, and use it.
  (for extra points, check to see if it actually points to an executable file. if not ignore)
  (if both specified, use OC)
• If neither OC nor KUBECTL env var are valid, then see if either oc or kubectl exist as executable files in current path. If only 1 exists, then use it. If two exist, then perhaps give priority to oc. If neither exist, print an informative diagnostic message and terminate.