cli: Don't use colon as delimiter in tab completion

Some strings (e.g. VRF) use a colon so this character should not be used as a delimiter by bash completion

Fixes https://github.com/SpriteLink/NIPAP/issues/422
Reference: http://stackoverflow.com/questions/10528695/how-to-reset-comp-wordbreaks-without-effecting-other-completion-script