Make external_gateway_nat_rules easier to understand
Make external_gateway_nat_rules easier to understand

Future patches will change these snat rules for address scopes.  I
found it much easier to understand the changes needed after formatting
these like this.

Change-Id: I8356e438334f8c1b6fdb497650a3b63835c612cf
Partially-Implements: blueprint address-scopes

noironetworks/neutron,jumpojoy/neutron,eayunstack/neutron,openstack/neutron,openstack/neutron,bigswitch/neutron,suneeth51/neutron,mmnelemane/neutron,jacknjzhou/neutron,neoareslinux/neutron,suneeth51/neutron,SamYaple/neutron,wenhuizhang/neutron,mattt416/neutron,swdream/neutron,watonyweng/neutron,dims/neutron,javaos74/neutron,paninetworks/neutron,huntxu/neutron,JianyuWang/neutron,wolverineav/neutron,cisco-openstack/neutron,asgard-lab/neutron,swdream/neutron,yanheven/neutron,paninetworks/neutron,wolverineav/neutron,sebrandon1/neutron,mahak/neutron,barnsnake351/neutron,bigswitch/neutron,JianyuWang/neutron,yanheven/neutron,klmitch/neutron,noironetworks/neutron,shahbazn/neutron,barnsnake351/neutron,mahak/neutron,eonpatapon/neutron,vivekanand1101/neutron,MaximNevrov/neutron,javaos74/neutron,chitr/neutron,cloudbase/neutron,glove747/liberty-neutron,eonpatapon/neutron,adelina-t/neutron,takeshineshiro/neutron,igor-toga/local-snat,apporc/neutron,sebrandon1/neutron,SamYaple/neutron,silenci/neutron,dims/neutron,jumpojoy/neutron,silenci/neutron,cisco-openstack/neutron,shahbazn/neutron,mattt416/neutron,sasukeh/neutron,mmnelemane/neutron,MaximNevrov/neutron,jacknjzhou/neutron,asgard-lab/neutron,wenhuizhang/neutron,igor-toga/local-snat,openstack/neutron,skyddv/neutron,klmitch/neutron,neoareslinux/neutron,apporc/neutron,chitr/neutron,sasukeh/neutron,huntxu/neutron,skyddv/neutron,mahak/neutron,glove747/liberty-neutron,watonyweng/neutron,dhanunjaya/neutron,dhanunjaya/neutron,takeshineshiro/neutron,vivekanand1101/neutron,cloudbase/neutron,adelina-t/neutron,eayunstack/neutron