Set nova.migration_interval to 3 seconds

Default value, 5 seconds, interacts badly with the default keepalive
default in httpd, 5 secs too, and make connections to fail often with
error:

('Connection aborted.', RemoteDisconnected('Remote end closed connection without response'))

when checking the migration status in nova.

Signed-off-by: Alfredo Moralejo <[email protected]>
(cherry picked from commit 9e2b1e4)

Author: amoralej

templates/00-default.conf

@@ -142,3 +142,6 @@ period = 900
 
 [watcher_cluster_data_model_collectors.storage]
 period = 900
+
+[nova]
+migration_interval = 3