Switch to using abc in the retargetable client
Switch to using abc in the retargetable client

abc is preferable to raising NotImplementedError because it will
prevent instantiation of a subclass that doesn't implement the
required methods rather than failing only when a missing method is
called.

Change-Id: I1043eefde675dd3b653d5b508be22cfd52d2fe8f
Implements: bp retargetable-functional-testing

suneeth51/neutron,apporc/neutron,javaos74/neutron,infobloxopen/neutron,SmartInfrastructures/neutron,skyddv/neutron,igor-toga/local-snat,mandeepdhami/neutron,waltBB/neutron_read,takeshineshiro/neutron,openstack/neutron,klmitch/neutron,openstack/neutron,mandeepdhami/neutron,JioCloud/neutron,Stavitsky/neutron,sebrandon1/neutron,NeCTAR-RC/neutron,magic0704/neutron,SamYaple/neutron,cisco-openstack/neutron,adelina-t/neutron,cloudbase/neutron-virtualbox,miyakz1192/neutron,asgard-lab/neutron,aristanetworks/neutron,neoareslinux/neutron,jerryz1982/neutron,vivekanand1101/neutron,rdo-management/neutron,waltBB/neutron_read,jerryz1982/neutron,SmartInfrastructures/neutron,mahak/neutron,shahbazn/neutron,shahbazn/neutron,cisco-openstack/neutron,openstack/neutron,eayunstack/neutron,noironetworks/neutron,apporc/neutron,blueboxgroup/neutron,rdo-management/neutron,Stavitsky/neutron,yanheven/neutron,antonioUnina/neutron,infobloxopen/neutron,paninetworks/neutron,neoareslinux/neutron,mahak/neutron,huntxu/neutron,JianyuWang/neutron,mmnelemane/neutron,swdream/neutron,SamYaple/neutron,silenci/neutron,pnavarro/neutron,JianyuWang/neutron,skyddv/neutron,bigswitch/neutron,cloudbase/neutron,paninetworks/neutron,MaximNevrov/neutron,NeCTAR-RC/neutron,takeshineshiro/neutron,alexandrucoman/vbox-neutron-agent,dims/neutron,mmnelemane/neutron,klmitch/neutron,sebrandon1/neutron,javaos74/neutron,cloudbase/neutron,wolverineav/neutron,blueboxgroup/neutron,silenci/neutron,bgxavier/neutron,eonpatapon/neutron,antonioUnina/neutron,aristanetworks/neutron,asgard-lab/neutron,JioCloud/neutron,adelina-t/neutron,jumpojoy/neutron,barnsnake351/neutron,jacknjzhou/neutron,wolverineav/neutron,wenhuizhang/neutron,noironetworks/neutron,magic0704/neutron,dhanunjaya/neutron,blueboxgroup/neutron,watonyweng/neutron,suneeth51/neutron,alexandrucoman/vbox-neutron-agent,glove747/liberty-neutron,jumpojoy/neutron,miyakz1192/neutron,yanheven/neutron,dims/neutron,wenhuizhang/neutron,vivekanand1101/neutron,sasukeh/neutron,eayunstack/neutron,pnavarro/neutron,glove747/liberty-neutron,yuewko/neutron,MaximNevrov/neutron,mattt416/neutron,eonpatapon/neutron,huntxu/neutron,sasukeh/neutron,cloudbase/neutron-virtualbox,chitr/neutron,swdream/neutron,mattt416/neutron,mahak/neutron,yuewko/neutron,dhanunjaya/neutron,barnsnake351/neutron,watonyweng/neutron,igor-toga/local-snat,bigswitch/neutron,chitr/neutron,bgxavier/neutron,jacknjzhou/neutron