[WFLY-2069] Switch between alternatives in a batch

* fix AlternativeAttributeCheckHandler as the check depends whether the
  operation is :write-attribute (and alternatives must not be defined) or
  :undefine-attribute (and an alternative *must* be defined)
* flag discovery-group-name and connector attributes to restart all
  services
* skip runtime update on HornetQ control object for these 2 attributes
  (that are not part of HornetQ management API)

The fix can be checked manually using the *`standalone-full-ha.xml`* configuration:

    [standalone@localhost:9990 /] /subsystem=messaging/hornetq-server=default/connection-factory=RemoteConnectionFactory:read-resource
    {
        "outcome" => "success",
        "result" => {
            ...
            "connector" => {"netty" => undefined},
            ...
        }
    }
    [standalone@localhost:9990 / #] batch
    [standalone@localhost:9990 / #] /subsystem=messaging/hornetq-server=default/connection-factory=RemoteConnectionFactory:undefine-attribute(name=connector)
    #1 /subsystem=messaging/hornetq-server=default/connection-factory=RemoteConnectionFactory:undefine-attribute(name=connector)
    [standalone@localhost:9990 / #] /subsystem=messaging/hornetq-server=default/connection-factory=RemoteConnectionFactory:write-attribute(name=discovery-group-name, value=dg-group1)
    #2 /subsystem=messaging/hornetq-server=default/connection-factory=RemoteConnectionFactory:write-attribute(name=discovery-group-name, value=dg-group1)
    [standalone@localhost:9990 / #] run-batch
    The batch executed successfully
    [standalone@localhost:9990 /] /subsystem=messaging/hornetq-server=default/connection-factory=RemoteConnectionFactory:read-resource
    {
        "outcome" => "success",
        "result" => {
            ...
            "connector" => undefined,
            ...
            "discovery-group-name" => "dg-group1",
            ...
        },
        "response-headers" => {
            "process-state" => "reload-required"
        }
    }
    [standalone@localhost:9990 /] /:reload
    {
        "outcome" => "success",
        "result" => undefined
    }