reregister node when they come back online

* Nodes are marked offline, then deleted; given enough time. Nodes can
come back for various reasions (i.e. netsplit). When they come back,
have them recreate the node Instance if AWX_AUTO_DEPROVISION_INSTANCES
is True. Otherwise, do nothing. The do nothing case will show up in the
logs as celery job tracebacks as they fail to be self aware.

awx/main/management/commands/provision_instance.py

@@ -2,7 +2,6 @@
 # All Rights Reserved
 
 from awx.main.models import Instance
-from awx.main.utils.pglock import advisory_lock
 from django.conf import settings
 
 from django.db import transaction
@@ -27,15 +26,12 @@ class Command(BaseCommand):
     def _register_hostname(self, hostname):
         if not hostname:
             return
-        with advisory_lock('instance_registration_%s' % hostname):
-            instance = Instance.objects.filter(hostname=hostname)
-            if instance.exists():
-                print("Instance already registered {}".format(instance[0].hostname))
-                return
-            instance = Instance(uuid=self.uuid, hostname=hostname)
-            instance.save()
-        print('Successfully registered instance {}'.format(hostname))
-        self.changed = True
+        (changed, instance) = Instance.objects.register(uuid=self.uuid, hostname=hostname)
+        if changed:
+            print('Successfully registered instance {}'.format(hostname))
+        else:
+            print("Instance already registered {}".format(instance.hostname))
+        self.changed = changed
 
     @transaction.atomic
     def handle(self, **options):