Change force_dhcp_release default to True
Change force_dhcp_release default to True

Historically it was was false because it requires the dnsmasq binary
'dhcp_release' which was not present in all distros.

Related to bug 970893

DocImpact

Change-Id: I4975d85a66fb930d6a56900dd569cec2a1874439

openstack/oslo.versionedobjects,citrix-openstack-build/oslo.versionedobjects