Remove useless code in L3 HA unit tests
Remove useless code in L3 HA unit tests

I added a helper function to make the server consider an agent
as down, might as well use it!

Change-Id: If1110de7f46ecb3dc2e72b3c62d7faeb0e71c586

MaximNevrov/neutron,huntxu/neutron,klmitch/neutron,openstack/neutron,cloudbase/neutron,noironetworks/neutron,wolverineav/neutron,mahak/neutron,yanheven/neutron,glove747/liberty-neutron,asgard-lab/neutron,eayunstack/neutron,mahak/neutron,apporc/neutron,eayunstack/neutron,noironetworks/neutron,MaximNevrov/neutron,mahak/neutron,glove747/liberty-neutron,klmitch/neutron,huntxu/neutron,wolverineav/neutron,cloudbase/neutron,dims/neutron,jumpojoy/neutron,chitr/neutron,yanheven/neutron,igor-toga/local-snat,apporc/neutron,dims/neutron,sebrandon1/neutron,openstack/neutron,openstack/neutron,sebrandon1/neutron,bigswitch/neutron,chitr/neutron,igor-toga/local-snat,asgard-lab/neutron,bigswitch/neutron,jumpojoy/neutron