help, makeapi: do not use hardcoded plugin package name
    
    Iterate over all plugin packages defined in the API to find the given
    topic module. The last module found has priority.
    
    This will allow topics to be defined in client-side plugins.
    
    https://fedorahosted.org/freeipa/ticket/4739
    
    Reviewed-By: David Kupka <dkupka@redhat.com>