[booth] `pcs booth create ip IP` shall not be allowed by the time config (`/etc/booth/booth.conf`) exists

If pcs is supposed to be a tool of user's convenience, it cannot be told
about an enforcement of booth configuring steps.

For a starter (this issue), `pcs booth create ip IP` command shall fail unless there
is a configuration already present (presumably in sync) across in-cluster systems.

Currently, it allows that, and booth IP is happily up and running, while
`booth-booth-service` cannot start ... for a missing configuration file.

Instead, user shall be redirected to where the initial configuration can be
prepared (and in dreams, it would interactively start start such a process
in a wizard-like manner right away).