Provide 'oc' binaries per platform

Instead of forcing the user to search, download and install the 'oc' library manually before being able to use port forwarding or log streaming, the platform-related binary could be installed automatically.
Possible implementation:

• define the oc binary URLs in stacks.yaml
• on openshift 3 plugin startup, check if oc binary is set in preferences
• if not set trigger background job to d/l oc binary matching current platform, and update preferences, else, do nothing.

manderse@redhat.com does it correspond to what you had in mind?