[V2] CLI host flag validation

[lynnemorrison]

We need to add a validator to the host flag in the CLI. For both kube and nonkube CLI we need to validate the host flag being passed. We need to understand what values are valid for the host flag.

[lynnemorrison]

@grs and @ssorj can you help me with what values are allowed in this field.

[nluaces]

My suggestion is to:

• Check if it is an IP
• If not, check if the length is equal or less than a number and that it only contains allowed characters: alphabetic characters (A-Z), numeric characters (0-9), the minus sign (-), and the period (.)

[grs]

I'm not sure I would add any constraints at this point. However I would agree with @nluaces above if we do.