If enable lbaas,service_plugins value is 'neutron_lbaas.services
.loadbalancer.plugin:LoadBalancerPluginv2'.
It throw warning for 'stevedore.named [-]Could not load neutron_lbaas
.services.loadbalancer.plugin.LoadBalancerPluginv2'

Closes-Bug: #1690694

Change-Id: I38d61405710ca88fbdb3cfd72a534986cf933195