doc: Improve table rendering using multi-row cells
doc: Improve table rendering using multi-row cells

Also, fix a nearby typo.  (nic -> nick)

Change-Id: If94b123f9b9291db1d889026de679d91645271bc

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