Decrease MariaDB wait timeout

This MariaDB setting uses the same timeout for SQL connections
as configured inside SQL Alchemy (pool_recycle) and prevent possibly
SQL session build up due to a large default setting (8 Hours).

Nova and Neutron are using a idle_timeout of 3600 by default,
for example
https://github.com/openstack/nova/blob/master/nova/db/sqlalchemy/api.py#L101
and respectively for Neutron
https://github.com/openstack/neutron/blob/stable/liberty/etc/neutron.conf#L761

Change-Id: I273739c3c10616cac148aeb839154e0fb3359bca
Closes-Bug: #1571682
(cherry picked from commit a1636b3bb3)

defaults/main.yml

@@ -45,7 +45,7 @@ galera_max_heap_table_size: 32M
 galera_tmp_table_size: 32M
 
 galera_file_limits: 65535
-galera_wait_timeout: 28800
+galera_wait_timeout: 3600
 
 ## innodb options
 galera_innodb_buffer_pool_size: 4096M

releasenotes/notes/decrease-mariadb-waittimeout-setting-ddaae0f2e1d31ee1.yaml

@@ -0,0 +1,5 @@
+---
+upgrade:
+   - The MariaDB wait_timeout setting is decreased to 1h to match the
+     SQL Alchemy pool recycle timeout, in order to prevent unnecessary
+     database session buildups.