Integrate scheduler into dispatcher main loop (#14067)

Dispatcher refactoring to get pg_notify publish payload
  as separate method

Refactor periodic module under dispatcher entirely
  Use real numbers for schedule reference time
  Run based on due_to_run method

Review comments about naming and code comments

awx/main/management/commands/run_dispatcher.py

@@ -3,15 +3,13 @@
 import logging
 import yaml
 
-from django.core.cache import cache as django_cache
+from django.conf import settings
 from django.core.management.base import BaseCommand
-from django.db import connection as django_connection
 
 from awx.main.dispatch import get_task_queuename
 from awx.main.dispatch.control import Control
 from awx.main.dispatch.pool import AutoscalePool
 from awx.main.dispatch.worker import AWXConsumerPG, TaskWorker
-from awx.main.dispatch import periodic
 
 logger = logging.getLogger('awx.main.dispatch')
 
@@ -21,6 +19,7 @@ class Command(BaseCommand):
 
     def add_arguments(self, parser):
         parser.add_argument('--status', dest='status', action='store_true', help='print the internal state of any running dispatchers')
+        parser.add_argument('--schedule', dest='schedule', action='store_true', help='print the current status of schedules being ran by dispatcher')
         parser.add_argument('--running', dest='running', action='store_true', help='print the UUIDs of any tasked managed by this dispatcher')
         parser.add_argument(
             '--reload',
@@ -42,6 +41,9 @@ class Command(BaseCommand):
         if options.get('status'):
             print(Control('dispatcher').status())
             return
+        if options.get('schedule'):
+            print(Control('dispatcher').schedule())
+            return
         if options.get('running'):
             print(Control('dispatcher').running())
             return
@@ -58,21 +60,11 @@ class Command(BaseCommand):
             print(Control('dispatcher').cancel(cancel_data))
             return
 
-        # It's important to close these because we're _about_ to fork, and we
-        # don't want the forked processes to inherit the open sockets
-        # for the DB and cache connections (that way lies race conditions)
-        django_connection.close()
-        django_cache.close()
-
-        # spawn a daemon thread to periodically enqueues scheduled tasks
-        # (like the node heartbeat)
-        periodic.run_continuously()
-
         consumer = None
 
         try:
             queues = ['tower_broadcast_all', 'tower_settings_change', get_task_queuename()]
-            consumer = AWXConsumerPG('dispatcher', TaskWorker(), queues, AutoscalePool(min_workers=4))
+            consumer = AWXConsumerPG('dispatcher', TaskWorker(), queues, AutoscalePool(min_workers=4), schedule=settings.CELERYBEAT_SCHEDULE)
             consumer.run()
         except KeyboardInterrupt:
             logger.debug('Terminating Task Dispatcher')