Cause: neutron-dist.conf file that sets default configuration values for Neutron contained service_provider setting for haproxy based load balancer plugin.
Consequence: This made it impossible to disable the service by modifying neutron.conf. It also made Neutron fail when an identical configuration setting from neutron.conf was uncommented.
Fix: service_providers section was removed from neutron-dist.conf.
Result: now service configuration is defined solely by neutron.conf.
Note for users who upgrade from previous versions: the following configuration setting should be manually added to /etc/neutron/neutron.conf to keep the load balancer service loaded:
service_provider = LOADBALANCER:Haproxy:neutron.services.loadbalancer.drivers.haproxy.plugin_driver.HaproxyOnHostPluginDriver:default