Fix inconsistent sentence on FlatDHCP description
Fix inconsistent sentence on FlatDHCP description

Change sentences order to clarify that DHCP servers are started
and configured by the node running nova-network.

Change-Id: I7e8b82375323ca61e90cef95ca84f66c4cb678e5
backport: none
Closes-Bug: #1157670

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