`verdi computer setup` could raise the duplicated message in a callback

Currently, in `verdi computer setup` if you use the same label of a computer that already exists, you'll notify at the very end of the command when all option are uselessly collected. 

One can simply add a callback function for `@options_computer.LABEL` to raise `click.BadParameter` in such cases.

Or even better, get a confirmation from user to do the same thing as `verdi computer duplicate`