Move class properties to instances for dhcp tests
Move class properties to instances for dhcp tests

Using class properties for tests always carries the risk of
conflicting use between test cases when tests are run in parallel.

Related-Bug: #1569507

Change-Id: I5868dd8e3c2293be26fd7c99338f7c979f727533

eayunstack/neutron,huntxu/neutron,huntxu/neutron,noironetworks/neutron,cloudbase/neutron,bigswitch/neutron,mahak/neutron,sebrandon1/neutron,noironetworks/neutron,openstack/neutron,sebrandon1/neutron,mahak/neutron,mahak/neutron,openstack/neutron,openstack/neutron,igor-toga/local-snat,eayunstack/neutron,igor-toga/local-snat,bigswitch/neutron,cloudbase/neutron