[AS7-6699] HornetQ backup mode

When HornetQ is configured to be a backup, it will start and remain
passive (its resources are not deployed, it does not accept any
connections, etc.)

For AS7 hornetq-server's children resources, that means that:
* read-attribute on runtime attributes is a no-op (returns undefined)
* execute an operation on a queue will throw an exception warning the
  user that HornetQ is in backup mode
* add active runtime r/o attribute to hornetq-server

For AS7 services, there are some substantial changes too.
HornetQService default does *not* start the HornetQ server. This is done
by JMSService. This means that any service must not depend on
HornetQService but JMSService to make sure that the server is
effectively started.
JMSService is started asynchronously and the server start is completed
when:
* the HornetQ server has been activated (immediately when it is a live
  node, or after failover if it is a backup)
* and the JMSServerManager is started (and can deploy JMS resources)

It is important for other services depending on messaging services
(queue, jms-queue, topic, connection-factory &
pooled-connection-factory) that these services must NOT be started
until a backup hornetq-server fails over.