[booth] `pcs constraint ticket add` does not care whether the ticket indeed exists

[jnpkrn]

Either pcs constraint ticket add or equivalent (see #227), for which
it would be particularly critical whether:

1. booth formation is up and running

2. when 1. doesn't hold but default booth configuration file still exists

3. whether the ticket is already defined by the time is being relied
   upon

When 1. or 2. holds while 3. doesn't:

• for pcs constraint ticket add, this shall be at least of a warning
  severity (non-blocking), but perhaps a blocking with error would be
  in order (unless overridden with --force or equivalent).

• for in-one-go shortcut, it shall be the latter right away

Similarly as with #222, user could be redirected to where the
ticket configuration can be carried (and in dreams, it would
interactively start such a process in a wizard-like manner
right away).

[tomjelinek]

Due to time constraints and other priorities, we haven't been able to implement these planned higher level booth commands which would be aware of the whole booth formation and which would be able to operate at a cluster level and booth formation level. For the users to be able to set booth at least somehow, only the node-level commands have been implemented. Those, even if not as comfortable as one may desire, provide a complete set of operations needed for configuring and managing booth.

The plans for the more comfortable booth management are still there. Unfortunately given current developer resources and backlog, it is a "blue-sky" project for now.