eventlet workaround to avoid import cycle issue

Do get_hub() before monkey_patch() to workaround issue with
import cycles in eventlet < 0.22.0;
Based on the worked-around in eventlet with patch
b756447bab

Also moved monkey_patch() up as far as possible to make sure all imports
get patched modules.

Closes-Bug: 1746136
Closes-Bug: 1745112

Conceptually cherry-picked from change I72c349e81dfc02136b22637c707ad4908c9f269e

Change-Id: I0ed736f30f8fd7a3ec046e5810b84b52910fa4c9

congress/server/congress_server.py

@@ -18,11 +18,20 @@
 from __future__ import print_function
 from __future__ import division
 from __future__ import absolute_import
+
+# NOTE(ekcs): monkey_patch ASAP to ensure all imports get patched modules
+import eventlet
+# NOTE(ekcs): get_hub() before monkey_patch() to workaround issue with
+# import cycles in eventlet < 0.22.0;
+# Based on the worked-around in eventlet with patch
+# https://github.com/eventlet/eventlet/commit/b756447bab51046dfc6f1e0e299cc997ab343701
+# For details please check https://bugs.launchpad.net/congress/+bug/1746136
+eventlet.hubs.get_hub()
+eventlet.monkey_patch()
+
 import socket
 import sys
 
-import eventlet
-eventlet.monkey_patch()
 from oslo_config import cfg
 from oslo_log import log as logging
 from oslo_service import service

releasenotes/notes/eventlet-cycle-103edf0cfbafd947.yaml

@@ -0,0 +1,10 @@
+---
+prelude: >
+fixes:
+  - |
+    On Ubuntu 16.04.3, an eventlet import cycle issue
+    can prevent Congress from starting. A workaround
+    is put in place in Congress to avoid this issue.
+    For more information, see the workaround released
+    in eventlet 0.22:
+    https://github.com/eventlet/eventlet/commit/b756447bab51046dfc6f1e0e299cc997ab343701