Fix rabbit_userid for multi node devstack
Fix rabbit_userid for multi node devstack

I43a231c9611b4cc2e390b603aa3bfb49c915bdc5 introduced a new setting
RABBIT_USERID but only set it if rabbit is enabled. In multi node
devstack the second node uses RABBIT_USERID but the service rabbit isn't
enabled on it.

Always set RABBIT_USERID, if a different message queue is used the
variable will just be ignored.

Change-Id: I8568bddda2a5c66235ecae23af58983ee94c720a

mc2014/devstack,j4/devstack,avvocatodemarchis/devstack,dtroyer/devstack,noironetworks/devstack,sequenceiq/devstack,thomasem/devstack,samgoon/devstack,TwinkleChawla/devstack,CloudServer/devstack,nuxeh/devstack,herrsechs/devstack,CloudServer/devstack,ozamiatin/devstack,sequenceiq/devstack,andrewrothstein/devstack,thomasem/devstack,parul24/devstack,prithivm/branch01,liuquansheng47/devstack,bq-xiao/devstack,wenhuizhang/devstack,affo/devstack,nuxeh/devstack,parul24/devstack,NaokiMiyata/devstack,NaokiMiyata/devstack,wenhuizhang/devstack,varunarya10/devstack,openstack-dev/devstack,rushiagr/devstack,dtroyer/devstack,eharney/devstack,ozamiatin/devstack,promptworks/devstack,bq-xiao/devstack,herrsechs/devstack,upadhyay-prashant/devstack,vishnugonela/devstack,mmasaki/devstack,samgoon/devstack,atulpatil301/devstack,mmasaki/devstack,sc68cal/devstack,richliu/devstack,flavio-fernandes/devstack,openstack-dev/devstack,liuquansheng47/devstack,Mahito/devstack,dirkmueller/devstack,sc68cal/devstack,mssumanth/devstack,bljgaurav/openstack-test,group-policy/devstack,HPCHub/devstack,bswartz/devstack,rushiagr/devstack,LoHChina/devstack,pacinete/devstack,andrewrothstein/devstack,eharney/devstack,bigswitch/devstack,pacinete/devstack,bigswitch/devstack,pombredanne/devstack,costingalan/devstack,kplus/devstack-moonshot,promptworks/devstack,avvocatodemarchis/devstack,noironetworks/devstack,neerja28/Devstack_GlusterFS,LoHChina/devstack,costingalan/devstack,pczerkas/devstack,neerja28/Devstack_GlusterFS,olivierlemasle/devstack,bljgaurav/openstack-test,atulpatil301/devstack,vsham20/devstack,TwinkleChawla/devstack,vishnugonela/devstack,pombredanne/devstack,flavio-fernandes/devstack,HPCHub/devstack,bswartz/devstack,BSJAIN92/OpenStack,group-policy/devstack,Mahito/devstack,BSJAIN92/OpenStack,nawawi/openstack,kplus/devstack-moonshot,j4/devstack,mc2014/devstack,mssumanth/devstack,varunarya10/devstack,affo/devstack,nawawi/openstack,dirkmueller/devstack,prithivm/branch01,pczerkas/devstack,upadhyay-prashant/devstack,richliu/devstack,vsham20/devstack,olivierlemasle/devstack