Move USE_CONSTRAINTS normalization back to stackrc
Move USE_CONSTRAINTS normalization back to stackrc

stackrc needs to do all of the initialization for situations (Grenade,
unstack.sh, etc) that do not run stack.sh

Change-Id: Ib8c7b923dde817b37f852515dd049fcf970b999a

dirkmueller/devstack,ozamiatin/devstack,LoHChina/devstack,NaokiMiyata/devstack,TwinkleChawla/devstack,atulpatil301/devstack,vsham20/devstack,NaokiMiyata/devstack,bswartz/devstack,pczerkas/devstack,liuquansheng47/devstack,pacinete/devstack,HPCHub/devstack,openstack-dev/devstack,flavio-fernandes/devstack,pombredanne/devstack,samgoon/devstack,pczerkas/devstack,flavio-fernandes/devstack,Mahito/devstack,j4/devstack,openstack-dev/devstack,mssumanth/devstack,dtroyer/devstack,eharney/devstack,group-policy/devstack,herrsechs/devstack,pacinete/devstack,HPCHub/devstack,costingalan/devstack,avvocatodemarchis/devstack,atulpatil301/devstack,mc2014/devstack,prithivm/branch01,eharney/devstack,richliu/devstack,j4/devstack,thomasem/devstack,vishnugonela/devstack,herrsechs/devstack,richliu/devstack,bswartz/devstack,TwinkleChawla/devstack,wenhuizhang/devstack,parul24/devstack,LoHChina/devstack,varunarya10/devstack,nawawi/openstack,prithivm/branch01,nawawi/openstack,CloudServer/devstack,avvocatodemarchis/devstack,mmasaki/devstack,bq-xiao/devstack,noironetworks/devstack,olivierlemasle/devstack,group-policy/devstack,mssumanth/devstack,liuquansheng47/devstack,bq-xiao/devstack,parul24/devstack,bigswitch/devstack,vishnugonela/devstack,varunarya10/devstack,Mahito/devstack,olivierlemasle/devstack,mc2014/devstack,noironetworks/devstack,mmasaki/devstack,pombredanne/devstack,wenhuizhang/devstack,ozamiatin/devstack,CloudServer/devstack,thomasem/devstack,dirkmueller/devstack,upadhyay-prashant/devstack,vsham20/devstack,upadhyay-prashant/devstack,bigswitch/devstack,dtroyer/devstack,costingalan/devstack,samgoon/devstack