[Event-engine] Make listener pool name configurable

* Now it is impossible to set the same
   pool name for queue listeners which use
   event engine. By default, it creates
   an unique pool named <hostname> so each
   event engine is in its own pool. Due to
   that and documentation of oslo.messaging,
   any message that comes to topic duplicates
   across all event engines.

 * But if they have the same pool name, the message
   will be delivered only to one of event-engines
   (by round-robin).

 * This patch adds a possibility to change listener pool
   name for each event-engine.

Change-Id: Iea83c461694a26d9cea810e6cc6169a0fe3f9f06

mistral/config.py

@@ -227,6 +227,13 @@ event_engine_opts = [
                'identifier. It is not necessarily a hostname, '
                'FQDN, or IP address.')
     ),
+    cfg.HostAddressOpt(
+        'listener_pool_name',
+        default='events',
+        help=_('Name of the event engine\'s listener pool. This can be an'
+               ' opaque identifier. It is used for identifying the group'
+               ' of event engine listeners in oslo.messaging.')
+    ),
     cfg.StrOpt(
         'topic',
         default='mistral_event_engine',

mistral/messaging.py

@@ -18,8 +18,8 @@ AMQP messages based on olso.messaging framework.
 """
 
 import abc
-import socket
 
+from oslo_config import cfg
 from oslo_log import log as logging
 import oslo_messaging
 from oslo_messaging.notify import dispatcher
@@ -30,6 +30,7 @@ from oslo_utils import timeutils
 import six
 
 LOG = logging.getLogger(__name__)
+CONF = cfg.CONF
 
 
 def handle_event(self, ctxt, publisher_id, event_type, payload, metadata):
@@ -91,7 +92,8 @@ def get_pool_name(exchange):
 
     :param exchange: exchange name
     """
-    pool_name = 'mistral-%s-%s' % (exchange, socket.gethostname())
+    pool_host = CONF.event_engine.listener_pool_name
+    pool_name = 'mistral-%s-%s' % (exchange, pool_host)
 
     LOG.debug("Listener pool name is %s", pool_name)