Logic proposal for --force flag to delete the validators during client bulk delete.

Final Logic:

If some validators match the regexp user provided to client bulk delete chef says `Following clients are validators and will not be deleted. You must specify --delete-validators to delete the validator clients.` and asks if the user wants to delete the matching non-validator clients.

When `--delete-validators` option is specified chef first asks if it's OK to delete the validators after that asks again to delete the non-validator clients.

Thoughts @opscode/client-eng & @curiositycasualty ?