add helptext to keystone_api_insecure
add helptext to keystone_api_insecure

Add helptext to this feature introduced in havana.

Change-Id: I403fb687f907618027b9e4d1e9b33bbf99b21efb
Closes-Bug: 1208608

openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,kairoaraujo/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,kairoaraujo/openstack-manuals,Akasurde/openstack-manuals,saeki-masaki/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,potsmaster/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,saeki-masaki/openstack-manuals,gongysh2004/openstack-manual,potsmaster/openstack-manuals,Akasurde/openstack-manuals,gongysh2004/openstack-manual,openstack/openstack-manuals