Comment 2 for bug 1497384

In the https://review.openstack.org/#/c/232141/

for l2, l3, dhcp and metadata agents I reserved flags name:
neutron_advanced_configuration/l2_agent_ha
neutron_advanced_configuration/l3_agent_ha
neutron_advanced_configuration/dhcp_agent_ha
neutron_advanced_configuration/metadata_agent_ha

This flags may be placed into neutron_advanced_configuration sub-tab into settings tab on UI