Simplify prepare_veth_pairs in functional tests
Simplify prepare_veth_pairs in functional tests

This change simplifies prepare_veth_pairs[1] as optional arguments are
never used by prepare_veth_pairs callers and uses create_veth.

This changes prepares to transform BaseLinuxTestCase[1] and
BaseOVSLinuxTestCase[1] methods in to helper methods.

[1] in neutron.tests.functional.agent.linux.base

Change-Id: I2e50057023bbf7575051f04b65cacc093338938a

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