def declare_unusable(identities)
      identities.each do |id|
        broker = @brokers_hash[id]
        raise Exception, "Cannot mark unknown broker #{id} unusable" unless broker
        broker.close(propagate = true, normal = false, log = false)
      end
    end
def declare_unusable(identities)
      identities.each do |id|
        broker = @brokers_hash[id]
        raise Exception, "Cannot mark unknown broker #{id} unusable" unless broker
        broker.close(propagate = true, normal = false, log = false)
      end
    end
Declare a broker client as unusable

 === Parameters
 identities(Array):: Identity of brokers

 === Return
 true:: Always return true

 === Raises
 Exception:: If identified broker is unknown