Use tornado's AnyThreadEventLoopPolicy

Since tornado 5.0 (with python 3), event loops by default have to be
created explicitly in each new thread. This commit reinstates the old
behavior in AWS and CWS.

http://www.tornadoweb.org/en/stable/asyncio.html#tornado.platform.asyncio.AnyThreadEventLoopPolicy

scripts/cmsAdminWebServer

@@ -32,6 +32,7 @@ gevent.monkey.patch_all()
 
 import logging
 import sys
+import tornado
 
 from cms import ConfigError, default_argument_parser
 from cms.db import test_db_connection
@@ -45,6 +46,11 @@ def main():
     """Parse arguments and launch service.
 
     """
+    if tornado.version_info >= (5, 0):
+        import asyncio
+        from tornado.platform.asyncio import AnyThreadEventLoopPolicy
+        asyncio.set_event_loop_policy(AnyThreadEventLoopPolicy())
+
     test_db_connection()
     success = default_argument_parser("Admins' web server for CMS.",
                                       AdminWebServer).run()

scripts/cmsContestWebServer

@@ -32,6 +32,7 @@ gevent.monkey.patch_all()
 
 import logging
 import sys
+import tornado
 
 from cms import ConfigError, default_argument_parser
 from cms.db import ask_for_contest, test_db_connection
@@ -45,6 +46,11 @@ def main():
     """Parse arguments and launch service.
 
     """
+    if tornado.version_info >= (5, 0):
+        import asyncio
+        from tornado.platform.asyncio import AnyThreadEventLoopPolicy
+        asyncio.set_event_loop_policy(AnyThreadEventLoopPolicy())
+
     test_db_connection()
     success = default_argument_parser("Contestants' web server for CMS.",
                                       ContestWebServer,