POC: replace our external log aggregation feature with rsyslog

- this change adds rsyslog (https://github.com/rsyslog/rsyslog) as
  a new service that runs on every AWX node (managed by supervisord)
  in particular, this feature requires a recent version (v8.38+) of
  rsyslog that supports the omhttp module
  (https://github.com/rsyslog/rsyslog-doc/pull/750)
- the "external_logger" handler in AWX is now a SysLogHandler that ships
  logs to the local UDP port where rsyslog is configured to listen (by
  default, 51414)
- every time a LOG_AGGREGATOR_* setting is changed, every AWX node
  reconfigures and restarts its local instance of rsyslog so that its
  fowarding settings match what has been configured in AWX
- unlike the prior implementation, if the external logging aggregator
  (splunk/logstash) goes temporarily offline, rsyslog will retain the
  messages and ship them when the log aggregator is back online
- 4xx or 5xx level errors are recorded at /var/log/tower/external.err

awx/main/tasks.py

@@ -72,7 +72,8 @@ from awx.main.utils import (get_ssh_version, update_scm_url,
                             ignore_inventory_group_removal, extract_ansible_vars, schedule_task_manager,
                             get_awx_version)
 from awx.main.utils.ansible import read_ansible_config
-from awx.main.utils.common import _get_ansible_version, get_custom_venv_choices
+from awx.main.utils.common import get_ansible_version, _get_ansible_version, get_custom_venv_choices
+from awx.main.utils.external_logging import reconfigure_rsyslog
 from awx.main.utils.safe_yaml import safe_dump, sanitize_jinja
 from awx.main.utils.reload import stop_local_services
 from awx.main.utils.pglock import advisory_lock
@@ -280,6 +281,12 @@ def handle_setting_changes(setting_keys):
     logger.debug('cache delete_many(%r)', cache_keys)
     cache.delete_many(cache_keys)
 
+    if any([
+        setting.startswith('LOG_AGGREGATOR')
+        for setting in setting_keys
+    ]):
+        reconfigure_rsyslog()
+
 
 @task(queue='tower_broadcast_all')
 def delete_project_files(project_path):