From now on, we will change default values for database connection pooling in each role
From now on, we will change default values for database connection pooling in each role

- ``openstack_db_max_overflow: 50`` - oslo.db's default
- ``openstack_db_max_pool_size: 5`` - oslo.db's default
- ``openstack_db_pool_timeout: 30`` - sqlalchemy's default
- ``openstack_db_connection_recycle_time: 600`` - long enough to not affect performance and short enough to avoid reaching max_connections limit during keepalived failovers in most cases.

Most of the default values look fine so I didn't want to overwrite them. However, if they won't be suitable for someone, they can change them here so it won't be needed to set them independently for each role

Change-Id: I5cccbbcf41fdf270e38c5b272638fe6d848de5c1

stackforge/os-ansible-deployment,openstack/openstack-ansible,openstack/openstack-ansible,stackforge/os-ansible-deployment