Change default behavior of create volume in Horizon

Issue

• I would like to change the default value of create_volume to False. By default the value is set to True in /var/lib/config-data/puppet-generated/horizon/etc/openstack-dashboard/local_settings:

LAUNCH_INSTANCE_DEFAULTS = {
    'config_drive': False,
    'create_volume': True,    <-----
    'disable_image': False,
    'disable_instance_snapshot': False,
    'disable_volume': False,
    'disable_volume_snapshot': False,
    'enable_scheduler_hints': True,
}