replace celery task decorators with a kombu-based publisher

this commit implements the bulk of `awx-manage run_dispatcher`, a new
command that binds to RabbitMQ via kombu and balances messages across
a pool of workers that are similar to celeryd workers in spirit.
Specifically, this includes:

- a new decorator, `awx.main.dispatch.task`, which can be used to
  decorate functions or classes so that they can be designated as
  "Tasks"
- support for fanout/broadcast tasks (at this point in time, only
  `conf.Setting` memcached flushes use this functionality)
- support for job reaping
- support for success/failure hooks for job runs (i.e.,
  `handle_work_success` and `handle_work_error`)
- support for auto scaling worker pool that scale processes up and down
  on demand
- minimal support for RPC, such as status checks and pool recycle/reload

awx/main/dispatch/control.py

@@ -0,0 +1,60 @@
+import logging
+import socket
+
+from django.conf import settings
+
+from awx.main.dispatch import get_local_queuename
+from kombu import Connection, Queue, Exchange, Producer, Consumer
+
+logger = logging.getLogger('awx.main.dispatch')
+
+
+class Control(object):
+
+    services = ('dispatcher', 'callback_receiver')
+    result = None
+
+    def __init__(self, service):
+        if service not in self.services:
+            raise RuntimeError('{} must be in {}'.format(service, self.services))
+        self.service = service
+        queuename = get_local_queuename()
+        self.queue = Queue(queuename, Exchange(queuename), routing_key=queuename)
+
+    def publish(self, msg, conn, host, **kwargs):
+        producer = Producer(
+            exchange=self.queue.exchange,
+            channel=conn,
+            routing_key=get_local_queuename()
+        )
+        producer.publish(msg, expiration=5, **kwargs)
+
+    def status(self, *args, **kwargs):
+        return self.control_with_reply('status', *args, **kwargs)
+
+    def running(self, *args, **kwargs):
+        return self.control_with_reply('running', *args, **kwargs)
+
+    def control_with_reply(self, command, host=None, timeout=5):
+        host = host or settings.CLUSTER_HOST_ID
+        logger.warn('checking {} {} for {}'.format(self.service, command, host))
+        reply_queue = Queue(name="amq.rabbitmq.reply-to")
+        self.result = None
+        with Connection(settings.BROKER_URL) as conn:
+            with Consumer(conn, reply_queue, callbacks=[self.process_message], no_ack=True):
+                self.publish({'control': command}, conn, host, reply_to='amq.rabbitmq.reply-to')
+                try:
+                    conn.drain_events(timeout=timeout)
+                except socket.timeout:
+                    logger.error('{} did not reply within {}s'.format(self.service, timeout))
+                    raise
+        return self.result
+
+    def control(self, msg, host=None, **kwargs):
+        host = host or settings.CLUSTER_HOST_ID
+        with Connection(settings.BROKER_URL) as conn:
+            self.publish(msg, conn, host)
+
+    def process_message(self, body, message):
+        self.result = body
+        message.ack()